Control method and system of shunt transformer based on new energy flexible direct current system

Abstract

The application provides a control method and system of a parallel transformer based on a new energy flexible direct current system, and the method comprises the following steps: selecting a transformer to be put into operation and a transformer line to be put into operation from a target transformer according to target demand, and confirming whether the flexible direct current system has charging conditions; controlling the transformer to be put into operation to perform a starting operation and controlling the transformer line to be put into operation to perform a putting-into operation according to a preset starting control strategy; controlling the transformer to be put into operation to perform an online parallel step according to a preset online parallel control strategy; and controlling the onshore station parallel transformer to perform a tapping self-synchronization step according to a preset tapping self-synchronization control strategy. The method can realize online parallel and parallel disconnection of any one of the transformers in the flexible direct current system parallel transformer, and improves the convenience of flexible direct current system maintenance, commissioning and power recovery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of direct current power transmission grid and equipment, in particular to a control method and system of parallel transformers based on a new energy flexible direct current system. BACKGROUND

[0002] At present, flexible direct current systems are generally used for long-distance power transmission of new energy projects in the middle and far sea areas and large-scale new energy bases. In order to improve the utilization rate of direct current transmission projects of new energy in the middle and far sea areas and large-scale new energy bases, two or more sets of transformers are designed on both sides of the flexible direct current system for parallel operation. However, the coordination of parallel transformers during the starting process of the direct current system has not been studied, the online input and output control strategy of parallel transformers has not been studied, and the synchronization strategy of the tap changer of parallel transformers has not been studied, so that the intelligent control of parallel transformers under the new energy flexible direct current system is low. SUMMARY

[0003] Therefore, the technical problem to be solved by the present application is to overcome the defect that there is no control method suitable for parallel transformers of a new energy flexible direct current system in the prior art, so as to provide a control method and system of parallel transformers based on a new energy flexible direct current system.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0005] In a first aspect, the present application provides a control method of parallel transformers based on a new energy flexible direct current system, comprising:

[0006] According to the target demand, a transformer to be put into operation and a transformer line to be put into operation are selected from target transformers, it is confirmed whether the flexible direct current system has charging conditions, the target transformers include onshore station parallel transformers and offshore station parallel transformers, the onshore station parallel transformers include first onshore transformers and second onshore transformers, the offshore station parallel transformers include first offshore transformers and second offshore transformers, and each transformer is correspondingly provided with two transformer lines;

[0007] According to a preset starting control strategy, the transformer to be put into operation is controlled to perform a starting operation, and the transformer line to be put into operation is controlled to perform an input operation;

[0008] According to a preset online parallel control strategy, the transformer to be put into operation is controlled to perform an online parallel step;

[0009] According to a preset tap changer self-synchronization control strategy, the onshore station parallel transformers are controlled to perform a tap changer self-synchronization step;

[0010] The step of controlling the transformer to be put into operation to perform online parallel connection according to the preset online parallel connection control strategy includes:

[0011] Close the first onshore transformer grid-side AC circuit breaker and the first offshore transformer grid-side AC circuit breaker.

[0012] The tap position information of the second onshore transformer is read, indicating that the second onshore transformer is in operation.

[0013] Adjust the tap of the first onshore transformer according to the tap position information of the second onshore transformer, and close the valve side circuit breaker of the first onshore transformer.

[0014] Optionally, controlling the transformer to be put into operation to perform a startup operation according to a preset startup control strategy includes:

[0015] When both the onshore and offshore parallel transformers are put into operation, the transformers to be put into operation are charged according to a preset charging sequence. The preset charging sequence includes: prioritizing the charging of the first onshore transformer and the first offshore transformer; after the charging of the first onshore transformer and the first offshore transformer is completed, the second onshore transformer and the second offshore transformer are charged; and the onshore and offshore parallel transformers are charged simultaneously.

[0016] When the first onshore transformer and the first offshore transformer are charged first, the bypass isolating switch of the charging resistor on the valve side of the onshore parallel transformer is closed.

[0017] Close the first onshore transformer grid-side AC circuit breaker and the first offshore transformer valve-side circuit breaker.

[0018] Adjust the tap of the first onshore transformer to close the valve-side circuit breaker of the first onshore transformer, thereby charging the converter valve of the onshore station;

[0019] Monitor the bypass DC voltage of the charging resistor. When the bypass DC voltage of the charging resistor is greater than the preset voltage value and the current on the valve side of the onshore station is less than the preset current value, bypass the charging resistor.

[0020] After the onshore station converter valve and the offshore station converter valve are successfully charged, the AC circuit breaker on the grid side of the second onshore transformer will be closed.

[0021] The first offshore transformer grid-side AC circuit breaker is closed to support the offshore station grid-side power grid.

[0022] Adjust the tap of the second onshore transformer to match the tap of the first onshore transformer;

[0023] Close the valve-side circuit breaker of the second offshore transformer and the valve-side circuit breaker of the second onshore transformer;

[0024] Close the circuit breaker on the grid side of the second offshore transformer.

[0025] Optionally, the step of controlling the transformer to be put into operation to perform online parallel connection according to a preset online parallel connection control strategy includes:

[0026] Close the first onshore transformer grid-side AC circuit breaker and the first offshore transformer grid-side AC circuit breaker.

[0027] The tap position information of the second onshore transformer is read, indicating that the second onshore transformer is in operation.

[0028] Adjust the tap of the first onshore transformer according to the tap position information of the second onshore transformer, and close the valve side circuit breaker of the first onshore transformer.

[0029] Optionally, the step of controlling the onshore station parallel transformer to perform tap self-synchronization according to a preset tap self-synchronization control strategy includes:

[0030] When the first onshore transformer is not charging, adjust the tap of the first onshore transformer to the preset position and close the valve side circuit breaker of the first onshore transformer.

[0031] When the second onshore transformer is put into operation, adjust the tap of the second onshore transformer to match the tap of the first onshore transformer.

[0032] Optionally, the control method for the parallel transformer based on the new energy flexible DC system further includes: when the sampling difference of the parallel transformer valve side voltage is greater than a preset value, comparing the parallel transformer valve side voltage with the ideal value of the valve side voltage calculated through the grid side voltage; when the ideal value is consistent with the sampling value, using the sampling value for tap adjustment and modulation ratio calculation.

[0033] Optionally, the control method for the parallel transformer based on the new energy flexible DC system further includes: when the tap of the second onshore transformer is inconsistent with the tap of the first onshore transformer, locking the continued adjustment function of the parallel transformer tap and performing self-synchronization on the tap; if the tap positions cannot be adjusted to be consistent within a preset time, locking the tap adjustment and switching the control mode of the parallel transformer tap to manual mode.

[0034] Optionally, the step of selecting the transformer to be put into operation and the transformer line to be put into operation from the target transformers according to the target requirements, and confirming whether the flexible DC system has charging conditions, includes:

[0035] Either all parallel transformers at the onshore station are put into operation, or any one of the parallel transformers at the onshore station is put into operation.

[0036] Either all parallel transformers at the offshore station are put into operation, or any one of the parallel transformers at the offshore station is put into operation.

[0037] Check whether the transformer to be put into operation has the necessary charging capabilities;

[0038] When the transformer to be put into operation has the charging conditions, select all or any one of the transformer lines corresponding to the transformer to be put into operation.

[0039] Check whether the transformer lines to be put into operation have charging capabilities;

[0040] When the transformer lines to be put into operation are ready for charging, check the number of transformers to be put into operation and the number of transformer lines to be put into operation.

[0041] When the number of transformers to be put into operation is greater than 0 and the number of transformer lines to be put into operation is greater than 0, the flexible DC system is confirmed to have the conditions for charging.

[0042] Secondly, embodiments of the present invention provide a control system for a parallel transformer based on a new energy flexible DC system, comprising:

[0043] The confirmation module is used to select the transformers to be put into operation and the transformer lines to be put into operation from the target transformers according to the target requirements, and to confirm whether the flexible DC system has the charging conditions. The target transformers include onshore station parallel transformers and offshore station parallel transformers. The onshore station parallel transformers include a first onshore transformer and a second onshore transformer. The offshore station parallel transformers include a first offshore transformer and a second offshore transformer. Each transformer is equipped with two transformer lines.

[0044] The input module is used to control the transformer to be put into operation to perform the start-up operation according to the preset start-up control strategy, and at the same time control the transformer line to be put into operation to perform the input operation.

[0045] The parallel module is used to control the transformers to be put into operation to perform online parallel steps according to the preset online parallel control strategy;

[0046] The synchronization module is used to control the onshore station parallel transformer to perform the tap self-synchronization step according to the preset tap self-synchronization control strategy;

[0047] The parallel module includes:

[0048] Close the first onshore transformer grid-side AC circuit breaker and the first offshore transformer grid-side AC circuit breaker.

[0049] The tap position information of the second onshore transformer is read, indicating that the second onshore transformer is in operation.

[0050] Adjust the tap of the first onshore transformer according to the tap position information of the second onshore transformer, and close the valve side circuit breaker of the first onshore transformer.

[0051] Thirdly, embodiments of the present invention provide a computer-readable storage medium storing computer instructions, which are used to cause the computer to execute the control method for parallel transformers based on a new energy flexible DC system as described in the first aspect of the present invention.

[0052] Fourthly, embodiments of the present invention provide a computer device, including: a memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the control method for parallel transformers based on new energy flexible DC systems described in the first aspect of the present invention.

[0053] The technical solution of this invention has the following advantages:

[0054] This invention provides a control method for parallel transformers based on a new energy flexible DC system, comprising: selecting transformers and transformer lines to be put into operation from target transformers according to target requirements, and confirming whether the flexible DC system has charging conditions; controlling the transformers to be put into operation to perform a start-up operation according to a preset start-up control strategy, and simultaneously controlling the transformer lines to be put into operation to perform an operation; controlling the transformers to be put into operation to perform an online parallel operation step according to a preset online parallel control strategy; controlling the onshore parallel transformers to perform a tap self-synchronization step according to a preset tap changer self-synchronization control strategy; and controlling the transformers to be put into operation to perform an online parallel operation step according to a preset online parallel control strategy, including: closing the AC circuit breaker on the grid side of the first onshore transformer and the AC circuit breaker on the grid side of the first offshore transformer; reading the tap position information of the second onshore transformer, indicating that the second onshore transformer is in an operational state; adjusting the tap of the first onshore transformer according to the tap position information of the second onshore transformer, and closing the valve side circuit breaker of the first onshore transformer. By setting control strategies under different operating conditions, the intelligence and reliability of the control of parallel transformers under the new energy flexible DC system are improved. Simultaneously, the design allows for the online paralleling and disconnection of any transformer in the parallel transformer of the flexible DC system, improving the convenience of maintenance, commissioning, and power restoration of the flexible DC system. Attached Figure Description

[0055] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0056] Figure 1 This is a system example diagram of a new energy flexible DC transmission system in an embodiment of the present invention;

[0057] Figure 2 This is a flowchart illustrating a specific example of a control method for a parallel transformer based on a new energy flexible DC system in an embodiment of the present invention.

[0058] Figure 3 This is a schematic diagram of a specific example of the control system of a parallel transformer based on a new energy flexible DC system in an embodiment of the present invention.

[0059] Figure 4 This is a composition diagram of a specific example of a computer device provided in an embodiment of the present invention. Detailed Implementation

[0060] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0062] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0063] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0064] like Figure 1 The diagram shown is an example of a flexible DC transmission system for new energy. Two or more transformers are designed to operate in parallel on each side of the flexible DC system. However, current research has not focused on the coordination of these parallel transformers during the DC system startup process, the online connection and disconnection control strategies for the parallel transformers, or the synchronization strategies for the tap changers of the parallel transformers.

[0065] Therefore, embodiments of the present invention provide a control method for a parallel transformer based on a new energy flexible DC system, such as... Figure 2 As shown, it includes the following steps:

[0066] Step S1: Select the transformers and transformer lines to be put into operation from the target transformers according to the target requirements, and confirm whether the flexible DC system has the charging conditions. The target transformers include onshore station parallel transformers and offshore station parallel transformers. The onshore station parallel transformers include the first onshore transformer T3 and the second onshore transformer T4, and the offshore station parallel transformers include the first offshore transformer T1 and the second offshore transformer T2. Each transformer has two corresponding transformer lines.

[0067] In one specific embodiment, step S1 includes:

[0068] Step S11: Select all parallel transformers at the onshore station to be put into operation, or select any one of the parallel transformers at the onshore station to be put into operation.

[0069] In this embodiment of the invention, the transformer to be put into operation is selected according to the target requirements, which can realize two working conditions: selecting all parallel transformers of the onshore station to be put into operation and selecting one transformer to be put into operation.

[0070] Furthermore, since the grid voltage flexible DC system is uncontrollable, the transformer inevitably generates inrush current during the charging process. The inrush current can be reduced by selecting phases for closing. To further reduce the impact of the inrush current, the onshore station can adopt a parallel transformer sequential charging control strategy.

[0071] Step S12: Select either all parallel transformers at the offshore station to be put into operation or select any one of the parallel transformers at the offshore station to be put into operation.

[0072] In this embodiment of the invention, the transformers to be put into operation are selected according to the target requirements, which can achieve two operating conditions: selecting all parallel transformers at the offshore station to be put into operation or selecting one transformer to be put into operation. In this embodiment of the invention, the parallel transformers at the onshore and offshore stations can be selected to operate in a variety of operating modes, which can be combined with four states: single transformer operation, dual transformer operation, dual-line transformer operation, and single-line transformer operation, thereby improving the flexibility of the flexible DC system operation.

[0073] Furthermore, the AC voltage at the offshore station is provided by a flexible DC system, which can control the AC voltage rise from 0kV to the rated voltage by setting the AC voltage boost rate. The inrush current of the parallel transformers at the offshore station can be controlled as follows: after all the parallel transformers at the offshore station are connected to converter valves, the flexible DC system unlocks and outputs AC voltage.

[0074] Step S13: Check whether the transformer to be put into operation has the conditions for charging.

[0075] In this embodiment of the invention, it is confirmed whether a transformer should be selected. If not selected, the check on whether the transformer is allowed to charge is skipped, and the selection of the line corresponding to the transformer is prohibited. If a transformer needs to be selected, it is checked whether the transformer has the conditions for charging based on the selection strategy. If not, the selection of the transformer and the line corresponding to the transformer are prohibited. The reason for the prohibition is displayed on the monitoring screen.

[0076] Step S14: When the transformer to be put into operation has the charging conditions, select all or any one of the transformer lines corresponding to the transformer to be put into operation to be put into operation.

[0077] In this embodiment of the invention, when the transformer to be put into operation has the charging conditions, the line to be put into operation for the transformer is selected according to the target requirements. It is possible to select both transformers of the transformer to be put into operation or to select one line to be put into operation.

[0078] Step S15: Check whether the transformer line to be put into operation has the conditions for charging.

[0079] In this embodiment of the invention, it is confirmed whether transformer line 1 is selected. If line 1 is not selected, the line check is skipped. If line 1 needs to be selected, the selection strategy checks whether line 1 has charging conditions. If it does not, charging of this line is prohibited and the reason for prohibition is displayed on the monitoring screen.

[0080] Further, confirm whether transformer line 2 is selected. If line 2 is not selected, skip the line check. If line 2 needs to be selected, the selection strategy checks whether line 2 has charging conditions. If it does not, prohibit charging on this line and display the prohibition on the monitoring screen along with the reason.

[0081] Step S16: When the transformer line to be put into operation has the charging conditions, check the number of transformers to be put into operation and the number of transformer lines to be put into operation.

[0082] In this embodiment of the invention, if the number of selected transformer lines is greater than 0, the transformer charging conditions are met; otherwise, transformer charging is prohibited, and the prohibition of charging and the reason are displayed on the monitoring screen.

[0083] Step S17: When the number of transformers to be put into operation is greater than 0 and the number of transformer lines to be put into operation is greater than 0, confirm that the flexible DC system has the conditions for charging.

[0084] In this embodiment of the invention, it is confirmed that the number of parallel transformers selected is greater than 0; otherwise, the flexible DC system will not have the conditions for charging.

[0085] Step S2: Control the transformer to be put into operation to perform the start-up operation according to the preset start-up control strategy, and at the same time control the transformer line to be put into operation to perform the connection operation.

[0086] In one specific embodiment, step S2 includes:

[0087] Step S21: When all onshore and offshore parallel transformers are put into operation, the transformers to be put into operation are charged according to the preset charging sequence. The preset charging sequence includes: first charging the first onshore transformer T3 and the first offshore transformer T1; after the first onshore transformer T3 and the first offshore transformer T1 are charged, the second onshore transformer T4 and the second offshore transformer T2 are charged; and the onshore and offshore parallel transformers are charged at the same time.

[0088] In this embodiment of the invention, when selecting the dual-transformer start-up mode, the design is based on the transformer inrush current situation, either simultaneous charging of both transformers or charging of priority transformer T1 or T3. The difference between simultaneous charging of both transformers and charging of priority transformer T1 or T3 is that it is not necessary to wait for priority charging transformer T1 or T3 to complete charging before charging transformer T2 or T4, but charging of priority transformer has a smaller impact on the grid inrush current.

[0089] Furthermore, priority line 1 is closed for charging, and then line 2 is closed for charging.

[0090] Step S22: When the first onshore transformer T3 and the first offshore transformer T1 are charged in priority, the bypass isolating switch Q13 of the valve side starting resistor R of the onshore station parallel transformer is closed.

[0091] In this embodiment of the invention, when the first onshore transformer T3 and the first offshore transformer T1 are selected to be charged first, and the second onshore transformer T4 and the second offshore transformer T2 are charged after the first onshore transformer T3 and the first offshore transformer T1 are charged, the bypass isolating switch Q13 of the valve side starting resistor R of the onshore station parallel transformer is closed.

[0092] Step S23: Close the AC circuit breakers Q17 and Q18 on the grid side of the first onshore transformer T3 and the valve side circuit breaker Q5 on the first offshore transformer T1.

[0093] In this embodiment of the invention, if the AC circuit breaker fails to close, the following judgment and sequence control are performed:

[0094] If the AC circuit breaker is not closed, set the "Do Not Close" sign for the AC circuit breaker on line 1 and send it to the monitoring backend. Then set line 2 as a charging line and charge through line 2.

[0095] Furthermore, if the AC circuit breaker trips after successfully closing, the cause of the fault is located by including the action information. If the fault is a line fault, the AC circuit breaker on line 1 is marked as prohibited from closing and the information is sent to the monitoring backend. The transformer is demagnetized and then charged via line 2. If the fault is a transformer fault, the transformer is marked as prohibited from charging and the information is sent to the monitoring backend.

[0096] Step S24: Adjust the tap of the first onshore transformer T3 to close the circuit breaker Q15 on the valve side of the first onshore transformer T3, thereby charging the converter valve of the onshore station.

[0097] In this embodiment of the invention, the AC circuit breakers Q17 and Q18 on the grid side of transformer T3 are successfully closed, and the tap changer is adjusted so that the valve-side voltage meets the charging requirements of the converter valve.

[0098] If a tap changer malfunctions during the adjustment process and cannot be adjusted to the voltage required by the converter valve, the relevant tap changer fault information is sent to the monitoring backend. A pop-up window in the monitoring backend indicates that transformer T4 needs to be switched to the start-up charging transformer. After confirmation by the operator, the sequential control process for transformer T4 is started, and the sequential control process for transformer T3 is paused. If transformer T3 needs to be shut down for isolation and defect handling, the operator will initiate the online exit sequence control process for the transformer.

[0099] Furthermore, the tap changer of transformer T3 is adjusted to the appropriate position, and the circuit breaker Q15 on the valve side charges the converter valve. If the circuit breaker Q15 on the valve side fails to close, the relevant fault is sent to the monitoring backend, the automatic sequential control process of the flexible DC system ends, and the automatic sequential control process of transformer T4 is started.

[0100] Furthermore, if the thermal accumulation calculation of the starting resistor R meets the charging time requirements of transformers T3 and T4, then transformers T3 and T4 are allowed to charge the converter valve. If the thermal accumulation calculation of the starting resistor R does not meet the charging conditions, the automatic sequential control process will terminate, and the cooling calculation function of the starting resistor R will be activated. After the cooling time is reached, the conditions for restarting the flexible DC system are met. The difference between the offshore station and the onshore station is that the offshore station charges the parallel transformers through the flexible DC system and does not have a starting resistor R.

[0101] Furthermore, if the valve-side circuit breaker or AC circuit breaker does not trip after the fault protection is activated, it should be determined whether to initiate remote tripping based on the cause of the fault.

[0102] Step S25: Monitor the bypass DC voltage of the starting resistor R. When the bypass DC voltage of the starting resistor R is greater than the preset voltage value and the current on the valve side of the land station is less than the preset current value, bypass the starting resistor R.

[0103] In this embodiment of the invention, if the bypass isolating switch Q13 fails to close, the relevant fault is sent to the monitoring backend, the automatic sequential control process of the flexible DC system ends, and the starting resistor R cooling calculation function is activated. After the cooling time is reached, it is ready to be recharged. If the valve-side circuit breaker and AC circuit breaker do not trip after the fault protection is activated, it is determined whether to activate the remote tripping function based on the cause of the fault.

[0104] Step S26: After the onshore station converter valve and the offshore station converter valve are successfully charged, the AC circuit breaker on the grid side of the second onshore transformer T4 is closed.

[0105] In this embodiment of the invention, after the onshore station converter valve and the offshore station converter valve are successfully charged, they enter the controllable charging process or unlock operation, start the automatic sequence control process of transformer T4, and close the AC circuit breakers Q19 and Q20 on the grid side of the second onshore transformer T4.

[0106] Furthermore, if the grid-side AC circuit breakers Q19 and Q20 fail to close, the following judgment and sequence control will be performed:

[0107] If the AC circuit breaker fails to close, the "Do Not Close" sign for AC circuit breaker 1 on line 1 is sent to the monitoring backend, and line 2 is set as the charging line for charging. If the AC circuit breaker successfully closes and then trips, the cause of the fault is located by analyzing the action information. If the fault is a line fault, the "Do Not Close" sign for AC circuit breaker 1 on line 1 is sent to the monitoring backend, and the transformer is demagnetized before charging via line 2. If the fault is a transformer fault, the "Do Not Charge" sign for the transformer is sent to the monitoring backend.

[0108] Step S27: Close the AC circuit breakers Q1 and Q2 on the grid side of the first offshore transformer T1 to support the offshore station grid side power grid.

[0109] In this embodiment of the invention, if the AC circuit breakers Q1 and Q2 on the transformer grid side are not closed, the relevant fault is sent to the monitoring background, the automatic sequential control process of the flexible DC system ends and the automatic sequential control process of transformer T2 is started.

[0110] Step S28: Adjust the tap of the second onshore transformer T4 to match the tap of the first onshore transformer T3.

[0111] In this embodiment of the invention, after the AC circuit breakers on the grid side of transformers T2 and T4 are successfully closed, the tap changer of transformer T4 is adjusted to match that of transformer T3. If a tap changer malfunctions during the adjustment process and cannot be adjusted to match that of transformer T3, the relevant fault is reported to the monitoring backend, and the automatic control process for transformer T4 is terminated. Furthermore, if transformer T4 needs to be shut down for defect isolation, an operator will initiate the online shutdown sequence control process for the transformer.

[0112] Step S29: Close the circuit breaker on the valve side of the second offshore transformer T2 and the circuit breaker on the valve side of the second onshore transformer T4.

[0113] In this embodiment of the invention, the tap changer of transformer T4 is adjusted to the appropriate position, and the valve-side circuit breakers Q6 and Q16 of transformer T2 and T4 are closed. If the valve-side circuit breakers Q6 and Q16 fail to close, the relevant fault is sent to the monitoring backend to initiate the sequence control termination. If the valve-side circuit breakers Q6 and Q16 trip after closing, the relevant fault is sent to the monitoring backend. If the valve-side circuit breaker and AC circuit breaker do not trip after the fault protection is activated, it is determined whether to initiate remote tripping based on the fault information.

[0114] Furthermore, the circuit breakers Q3 and Q4 on the grid side of the second offshore transformer T2 were closed.

[0115] In this embodiment of the invention, faults will inevitably occur during the charging process of the parallel transformer. In order to improve the intelligence of automatic control, the fault cause is located based on the AC protection action and DC protection action information: AC line fault, transformer fault, DC system fault. Based on the fault information, fault isolation, automatic sequential control step jump, and automatic sequential control termination of the charging process are determined.

[0116] Specifically, when the AC protection action information indicates an AC line fault, the line circuit breaker and isolating switch are opened to isolate the fault point and lock the line, thus enabling the transformer to operate under charging conditions. When the AC protection action information indicates a transformer fault, the circuit breaker and isolating switch related to the transformer are opened to isolate the fault point and lock the transformer, thus preventing the transformer from operating under charging conditions. Based on DC protection action information, the flexible DC system is shut down and all circuit breakers are locked, preventing the system from starting.

[0117] Furthermore, tap faults inevitably occur during the charging process of the parallel transformer, which may cause the valve-side voltage to be too low to charge the converter valve. After setting the waiting time according to the automatic sequence control step sequence, the automatic sequence control process of the tap fault transformer is paused, and the step sequence is switched to use the parallel transformer to charge the converter valve.

[0118] Step S3: Control the transformer to be put into operation to perform online parallel operation steps according to the preset online parallel control strategy.

[0119] In one specific embodiment, step S3 includes:

[0120] Step S31: Close the AC circuit breakers Q17 and Q18 on the grid side of the first onshore transformer T3 and Q1 and Q2 on the grid side of the first offshore transformer T1.

[0121] In this embodiment of the invention, if the AC circuit breaker fails to close, the following judgment and sequence control are performed:

[0122] If the AC circuit breaker is not closed, set the "Do Not Close" sign for the AC circuit breaker on line 1 and send it to the monitoring backend. Then set line 2 as a charging line and charge through line 2.

[0123] Furthermore, if the AC circuit breaker trips after successfully closing, the cause of the fault is located by including the action information. If the fault is a line fault, the AC circuit breaker on line 1 is marked as prohibited from closing and the information is sent to the monitoring backend. The transformer is demagnetized and then charged via line 2. If the fault is a transformer fault, the transformer is marked as prohibited from charging and the information is sent to the monitoring backend.

[0124] Step S32: Read the tap information of the second onshore transformer T4. The second onshore transformer T4 is in operation.

[0125] In this embodiment of the invention, the AC circuit breakers Q17 and Q18 on the grid side of the first onshore transformer T3 are successfully closed, the tap position information of the already running second onshore transformer T4 is read, and the tap positions are adjusted to be consistent;

[0126] Furthermore, if a tap changer malfunctions during the adjustment process and cannot be adjusted to the voltage required by the converter valve, the relevant fault is reported to the monitoring backend, and the sequential control process of the first onshore transformer T3 is suspended. If the first onshore transformer T3 needs to be shut down for defect isolation, operators will initiate the online exit sequence control process for the transformer.

[0127] Step S33: Adjust the tap of the first onshore transformer T3 according to the tap position information of the second onshore transformer T4, and close the circuit breaker Q15 on the valve side of the first onshore transformer T3.

[0128] In this embodiment of the invention, the tap of the first onshore transformer T3 is adjusted to the appropriate position, and the valve-side circuit breaker Q15 is closed. If the transformer valve-side circuit breaker Q15 fails to close, the relevant fault is sent to the monitoring backend to start the sequence control termination. If the transformer valve-side circuit breaker Q15 trips after closing, the relevant fault is sent to the monitoring backend.

[0129] Specifically, when a parallel transformer is disconnected online, the new energy system needs to switch and isolate it, and then automatically control the circuit breaker and disconnector of the transformer to open.

[0130] In one embodiment, the online parallel operation of transformers at onshore and offshore stations can be configured in two modes: dual-line operation or single-line operation, thereby improving the flexibility of online parallel operation.

[0131] To avoid impacting transformer paralleling and disconnection by renewable energy systems at offshore stations, the renewable energy systems connected to the transformers must be disconnected before online paralleling and disconnection of transformers. Automatic sequential control of the online paralleling and disconnection of transformers must then be implemented. The renewable energy systems are then put into operation only after the automatic sequential control is complete. This embodiment improves the convenience of DC system operation and maintenance through online paralleling and disconnection of transformers.

[0132] Step S4: Control the onshore station parallel transformer to perform the tap self-synchronization step according to the preset tap self-synchronization control strategy.

[0133] In one specific embodiment, step S4 includes:

[0134] Step S41: When the first land transformer T3 is not charged, adjust the tap of the first land transformer T3 to the preset position and close the valve side circuit breaker Q15 of the first land transformer T3.

[0135] In this embodiment of the invention, when the first onshore transformer T3 is not charging, the tap changer of the step-down transformer is adjusted to the lowest or middle position of the valve-side voltage. If the first onshore transformer T3 is charging first, the tap changer of the first onshore transformer T3 is adjusted to a suitable position using the valve-side voltage adjustment function, and the valve-side circuit breaker Q15 is closed to charge the converter valve.

[0136] Step S42: When the second land transformer T4 is put into operation, adjust the tap of the second land transformer T4 to match the tap of the first land transformer T3.

[0137] In this embodiment of the invention, when the second land transformer T4 is put into operation, the tap position of the second land transformer T4 is preferentially put into operation in the first land transformer T3. During the following process, the valve side voltage and modulation ratio are not used to control the tap position of the second land transformer T4.

[0138] Step S43: When the sampling difference of the valve side voltage of the parallel transformer is greater than the preset value, the valve side voltage of the parallel transformer is compared with the ideal value of the valve side voltage calculated through the grid side voltage. When the ideal value is consistent with the sampling value, the sampling value is used for tap adjustment and modulation ratio calculation.

[0139] In this embodiment of the invention, after the parallel transformer is in operation, to improve the reliability of the valve-side voltage, it is necessary to select the valve-side voltage of the parallel transformer. The parallel transformer achieves consistency in valve-side voltage and modulation ratio by adjusting the tap changer. To achieve the above requirements, the tap changers of the parallel transformer need to be adjusted to be consistent. Since the parallel transformer has two valve-side voltage measurement points, a reference calculation point for the valve-side voltage of the tap changer needs to be selected. The selection of the valve-side voltage of the parallel transformer is based on the quality of the valve-side voltage sampling value, comparison of the parallel transformer valve-side voltage, and comparison of the valve-side voltage with the grid-side voltage, thus selecting the valve-side voltage used for tap changer control.

[0140] Specifically, valve-side voltage sampling values ​​with abnormal quality are not included in the comparison calculation; valve-side voltage is not included in the comparison calculation when the transformer is not charged; when the valve-side voltage sampling difference of parallel transformers is less than a set value, the average valve-side voltage is used to calculate the valve-side voltage and modulation ratio.

[0141] When the sampling difference of the valve-side voltage of the parallel transformer is greater than the set value, the valve-side voltage is compared with the ideal value of the valve-side voltage calculated through the grid-side voltage. When the calculated value is consistent with the sampling value, it can be used for tap adjustment and modulation ratio calculation.

[0142] Step S44: When the tap of the second onshore transformer T4 is inconsistent with the tap of the first onshore transformer T3, the function of continuing to adjust the tap of the parallel transformer is locked, and the tap is self-synchronized. If the tap positions cannot be adjusted to be consistent within a preset time, the tap adjustment is locked and the control mode of the parallel transformer tap is switched to manual mode.

[0143] In this embodiment of the invention, the transformer is determined to be operational based on a comprehensive assessment of the grid-side voltage exceeding a set value, the valve-side voltage exceeding a set value, and the closing positions of valve-side circuit breakers Q15 and Q16. The target tap position is then generated based on the order in which the transformers have been operational. After the transformers are connected in parallel online, there are two strategies for adjusting the tap position: both parallel transformers can be adjusted based on the valve-side voltage and modulation ratio; the parallel transformers adjust the tap position following the already operational transformers.

[0144] In one embodiment, the tap positions of the parallel transformers must not differ by more than one tap. When the online parallel transformers are connected, the selected valve-side voltage and modulation ratio already meet the operating requirements of the DC system and will not generate a tap adjustment command. The online parallel transformers follow the tap positions of the already running transformers and are adjusted to be consistent.

[0145] The system determines whether a transformer is operational based on a comprehensive assessment of factors including grid-side voltage exceeding a set value, valve-side voltage exceeding a set value, and the closing position of the valve-side circuit breaker. The target tap position is then generated based on the order in which the transformers have been operational. After transformers are connected in parallel online, there are two strategies for adjusting the tap position: both parallel transformers can be adjusted based on valve-side voltage and modulation ratio. Parallel transformers adjust their taps following those of the already operational transformers.

[0146] This embodiment achieves consistent control of the taps of the parallel transformers by tap following, achieves high reliability of the modulation ratio by selecting the valve side voltage, and avoids tap position differences in the parallel transformers by interlocking the tap faults of the parallel transformers.

[0147] This invention provides a control method for parallel transformers based on a new energy flexible DC system, comprising: selecting transformers and transformer lines to be put into operation from target transformers according to target requirements, and confirming whether the flexible DC system has charging conditions; controlling the transformers to be put into operation to perform a start-up operation according to a preset start-up control strategy, and simultaneously controlling the transformer lines to be put into operation to perform an operation; controlling the transformers to be put into operation to perform an online parallel operation step according to a preset online parallel control strategy; controlling the onshore parallel transformers to perform a tap self-synchronization step according to a preset tap changer self-synchronization control strategy; and controlling the transformers to be put into operation to perform an online parallel operation step according to a preset online parallel control strategy, including: closing the AC circuit breaker on the grid side of the first onshore transformer and the AC circuit breaker on the grid side of the first offshore transformer; reading the tap position information of the second onshore transformer, indicating that the second onshore transformer is in an operational state; adjusting the tap of the first onshore transformer according to the tap position information of the second onshore transformer, and closing the valve side circuit breaker of the first onshore transformer. By setting control strategies under different operating conditions, the intelligence and reliability of the control of parallel transformers under the new energy flexible DC system are improved. Simultaneously, the design allows for the online paralleling and disconnection of any transformer in the parallel transformer of the flexible DC system, improving the convenience of maintenance, commissioning, and power restoration of the flexible DC system.

[0148] This invention also provides a control system for a parallel transformer based on a new energy flexible DC system, such as... Figure 3 As shown, it includes:

[0149] Confirmation module 1 is used to select transformers and transformer lines to be put into operation from the target transformers according to the target requirements, and to confirm whether the flexible DC system has charging conditions. The target transformers include onshore parallel transformers and offshore parallel transformers. The onshore parallel transformers include a first onshore transformer and a second onshore transformer, and the offshore parallel transformers include a first offshore transformer and a second offshore transformer. Each transformer corresponds to two transformer lines. For details, please refer to the relevant description of step S1 in the above embodiment, which will not be repeated here.

[0150] The input module 2 is used to control the transformer to be put into operation to perform the start-up operation according to the preset start-up control strategy, and at the same time control the transformer line to be put into operation to perform the input operation. For details, please refer to the relevant description of step S2 in the above embodiment, which will not be repeated here.

[0151] Parallel module 3 is used to control the transformer to be put into operation to perform online parallel steps according to the preset online parallel control strategy.

[0152] Parallel module 3 includes: closing the AC circuit breaker on the grid side of the first onshore transformer and the AC circuit breaker on the grid side of the first offshore transformer; reading the tap position information of the second onshore transformer, indicating that the second onshore transformer is in operation; adjusting the tap changer of the first onshore transformer according to the tap position information of the second onshore transformer, and closing the valve side circuit breaker of the first onshore transformer. For details, please refer to the relevant description of step S3 in the above embodiments, which will not be repeated here.

[0153] Synchronization module 4 is used to control the onshore station parallel transformer to perform the tap self-synchronization step according to the preset tap self-synchronization control strategy. For details, please refer to the relevant description of step S4 in the above embodiments, which will not be repeated here.

[0154] This invention provides a computer device, such as... Figure 4 As shown, the device may include a processor 81 and a memory 82, wherein the processor 81 and the memory 82 may be connected via a bus or other means. Figure 4 Take a bus connection as an example.

[0155] Processor 81 can be a central processing unit (CPU). Processor 81 can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or combinations of the above types of chips.

[0156] The memory 82, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs, non-transitory computer-executable programs, and modules, such as the corresponding program instructions / modules in the embodiments of the present invention. The processor 81 executes various functional applications and data processing by running the non-transitory software programs, instructions, and modules stored in the memory 82, thereby realizing the control method of the parallel transformer based on the new energy flexible DC system in the above method embodiments.

[0157] The memory 82 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created by the processor 81, etc. Furthermore, the memory 82 may include high-speed random access memory and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, the memory 82 may optionally include memory remotely located relative to the processor 81, and these remote memories may be connected to the processor 81 via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, mobile communication networks, and combinations thereof.

[0158] One or more modules are stored in memory 82, and when executed by processor 81, they perform actions such as... Figures 1-2 The control method for parallel transformers based on a new energy flexible DC system is shown.

[0159] For specific details regarding the aforementioned computer equipment, please refer to the relevant documentation. Figures 1-2 The relevant descriptions and effects in the illustrated embodiments are for understanding purposes only and will not be repeated here.

[0160] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk drive (HDD), or solid-state drive (SSD), etc.; the storage medium can also include combinations of the above types of memory.

[0161] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A control method for a parallel transformer based on a new energy flexible DC system, characterized in that, include: Based on the target requirements, select the transformers and transformer lines to be put into operation from the target transformers, and confirm whether the flexible DC system has the charging conditions. The target transformers include onshore station parallel transformers and offshore station parallel transformers. The onshore station parallel transformers include a first onshore transformer and a second onshore transformer. The offshore station parallel transformers include a first offshore transformer and a second offshore transformer. Each transformer is equipped with two transformer lines. The system controls the transformers to be put into operation to perform startup operations according to the preset startup control strategy, and simultaneously controls the transformer lines to be put into operation to perform connection operations. The transformer to be put into operation is controlled to perform online parallel connection steps according to the preset online parallel connection control strategy; The onshore station parallel transformer is controlled to perform tap self-synchronization steps according to the preset tap self-synchronization control strategy; The step of controlling the transformer to be put into operation to perform online parallel connection according to the preset online parallel connection control strategy includes: Close the first onshore transformer grid-side AC circuit breaker and the first offshore transformer grid-side AC circuit breaker. The tap position information of the second onshore transformer is read, indicating that the second onshore transformer is in operation. Adjust the tap of the first onshore transformer according to the tap position information of the second onshore transformer, and close the valve side circuit breaker of the first onshore transformer.

2. The control method for parallel transformers based on a new energy flexible DC system according to claim 1, characterized in that, The step of controlling the transformer to be put into operation to perform a startup operation according to a preset startup control strategy includes: When both the onshore and offshore parallel transformers are put into operation, the transformers to be put into operation are charged according to a preset charging sequence. The preset charging sequence includes: prioritizing the charging of the first onshore transformer and the first offshore transformer; after the charging of the first onshore transformer and the first offshore transformer is completed, the second onshore transformer and the second offshore transformer are charged; and the onshore and offshore parallel transformers are charged simultaneously. When the first onshore transformer and the first offshore transformer are charged first, the bypass isolating switch of the charging resistor on the valve side of the onshore parallel transformer is closed. Close the first onshore transformer grid-side AC circuit breaker and the first offshore transformer valve-side circuit breaker. Adjust the tap of the first onshore transformer to close the valve-side circuit breaker of the first onshore transformer, thereby charging the converter valve of the onshore station; Monitor the bypass DC voltage of the charging resistor. When the bypass DC voltage of the charging resistor is greater than the preset voltage value and the current on the valve side of the onshore station is less than the preset current value, bypass the charging resistor. After the onshore station converter valve and the offshore station converter valve are successfully charged, the AC circuit breaker on the grid side of the second onshore transformer will be closed. The first offshore transformer grid-side AC circuit breaker is closed to support the offshore station grid-side power grid. Adjust the tap of the second onshore transformer to match the tap of the first onshore transformer; Close the valve-side circuit breaker of the second offshore transformer and the valve-side circuit breaker of the second onshore transformer; Close the circuit breaker on the grid side of the second offshore transformer.

3. The control method for parallel transformers based on a new energy flexible DC system according to claim 1, characterized in that, The step of controlling the onshore station parallel transformer to perform tap self-synchronization according to the preset tap self-synchronization control strategy includes: When the first onshore transformer is not charging, adjust the tap of the first onshore transformer to the preset position and close the valve side circuit breaker of the first onshore transformer. When the second onshore transformer is put into operation, adjust the tap of the second onshore transformer to match the tap of the first onshore transformer.

4. The control method for parallel transformers based on a new energy flexible DC system according to claim 3, characterized in that, Also includes: When the sampling difference of the valve side voltage of the parallel transformer is greater than the preset value, the valve side voltage of the parallel transformer is compared with the ideal value of the valve side voltage calculated by the grid side voltage. When the ideal value is consistent with the sampling value, the sampling value is used for tap adjustment and modulation ratio calculation.

5. The control method for parallel transformers based on a new energy flexible DC system according to claim 4, characterized in that, Also includes: When the tap of the second onshore transformer is inconsistent with the tap of the first onshore transformer, the function of continuing to adjust the tap of the parallel transformer is locked, and the tap is self-synchronized. If the tap positions cannot be adjusted to be consistent within a preset time, the tap adjustment is locked and the control mode of the parallel transformer tap is switched to manual mode.

6. The control method for parallel transformers based on a new energy flexible DC system according to claim 1, characterized in that, The step of selecting transformers and transformer lines to be put into operation from the target transformers according to the target requirements, and confirming whether the flexible DC system has charging conditions, includes: Either all parallel transformers at the onshore station are put into operation, or any one of the parallel transformers at the onshore station is put into operation. Either all parallel transformers at the offshore station are put into operation, or any one of the parallel transformers at the offshore station is put into operation. Check whether the transformer to be put into operation has the necessary charging capabilities; When the transformer to be put into operation has the charging conditions, select all or any one of the transformer lines corresponding to the transformer to be put into operation. Check whether the transformer lines to be put into operation have charging capabilities; When the transformer lines to be put into operation are ready for charging, check the number of transformers to be put into operation and the number of transformer lines to be put into operation. When the number of transformers to be put into operation is greater than 0 and the number of transformer lines to be put into operation is greater than 0, the flexible DC system is confirmed to have the conditions for charging.

7. A control system for a parallel transformer based on a new energy flexible DC system, characterized in that, include: The confirmation module is used to select the transformers to be put into operation and the transformer lines to be put into operation from the target transformers according to the target requirements, and to confirm whether the flexible DC system has the charging conditions. The target transformers include onshore station parallel transformers and offshore station parallel transformers. The onshore station parallel transformers include a first onshore transformer and a second onshore transformer. The offshore station parallel transformers include a first offshore transformer and a second offshore transformer. Each transformer is equipped with two transformer lines. The input module is used to control the transformer to be put into operation to perform the start-up operation according to the preset start-up control strategy, and at the same time control the transformer line to be put into operation to perform the input operation. The parallel module is used to control the transformers to be put into operation to perform online parallel steps according to the preset online parallel control strategy; The synchronization module is used to control the onshore station parallel transformer to perform the tap self-synchronization step according to the preset tap self-synchronization control strategy; The parallel module includes: Close the first onshore transformer grid-side AC circuit breaker and the first offshore transformer grid-side AC circuit breaker. The tap position information of the second onshore transformer is read, indicating that the second onshore transformer is in operation. Adjust the tap of the first onshore transformer according to the tap position information of the second onshore transformer, and close the valve side circuit breaker of the first onshore transformer.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing the computer to execute the control method for parallel transformers based on a new energy flexible DC system as described in any one of claims 1-6.

9. A computer device, characterized in that, include: The system includes a memory and a processor, which are interconnected. The memory stores computer instructions, and the processor executes these computer instructions to perform the control method for a parallel transformer based on a new energy flexible DC system as described in any one of claims 1-6.

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