A DC fault self-clearing method for a new energy island power grid transmission system

Abstract

The present invention discloses a method for self-clearing DC faults in a new energy island power grid transmission system. The sending end adopts a constant AC voltage and frequency control strategy, and there is only one receiving end that adopts a constant DC voltage control strategy, while the remaining receiving ends adopt a constant active power control strategy. At the same time, each pole of the flexible DC converter station at the sending end real-time detects the DC current flowing out of this pole, and each pole of the flexible DC converter station at the receiving end real-time detects the DC current flowing into this pole. After detecting the occurrence of a DC fault, the DC fault is automatically cleared according to their respective control strategies, and the energy balance of the sending end island is achieved in cooperation with the AC energy consumption at the sending end. It solves the technical problems of coordinated control between flexible DC and new energy, power surplus, and self-clearing of DC faults on the DC side, and improves the power regulation ability and system stability of the new energy island power grid transmission system.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible DC power transmission, and particularly to a DC fault self-clearing method for a new energy island power grid transmission system. Background Art

[0002] Most new energy bases are built in remote areas with low load levels and weak grid structures, and there is an obvious demand for stable external transmission of new energy islands. Flexible DC power transmission has the characteristics of flexibility, controllability, high efficiency, etc., and is one of the important power transmission means for new energy external transmission. For the sending end, the flexible DC converter can provide a stable AC voltage for the new energy power plant, can operate in an island mode, and can quickly and dynamically compensate sufficiently to reduce the risk of new energy units tripping off the grid and improve the utilization rate of new energy. For the receiving end, flexible DC has no commutation failure problem and can provide dynamic reactive power compensation, which is of great significance for effectively solving problems such as the stability of multi-DC fed AC grid and withstanding severe grid faults.

[0003] DC fault ride-through technology is a key technology to be considered when the flexible DC power transmission system is applied to new scenarios of large-scale onshore renewable energy development and long-distance external transmission. The current DC fault ride-through technology still has the following technical problems: 1) The energy storage of the sub-module capacitors in the converter valve is small, and the over-current and over-voltage capabilities are weak. At the moment of DC fault, the new energy power regulation ability is weak and the speed is slow, making it difficult to quickly and significantly solve the energy imbalance problem between the AC and DC sides; 2) Longer-distance and larger-capacity overhead lines will reduce the arc extinction speed and even cause the arc extinction to not be completed within the set deionization time, affecting the stability of the system; 3) In the new energy island transmission, the AC voltage and frequency need to be constructed by flexible DC. During the DC fault clearing period, the flexible DC still needs to actively control the fault current through a negative voltage output strategy, and the control difficulty is large. Summary of the Invention

[0004] The present invention provides a DC fault self-clearing method for a new energy island power grid transmission system, which gives full play to the advantages of flexible DC, solves the technical problems of coordinated control between flexible DC and new energy, power surplus, and self-clearing of DC faults on the DC side, and can realize the large-capacity and long-distance transmission of a new energy island power grid through a true bipolar flexible DC overhead line.

[0005] In view of this, the first aspect of the present invention provides a DC fault self-clearing method for a new energy island power grid transmission system, including:

[0006] S1. Build a transmission system for a new energy island power grid. The transmission system for the new energy island power grid includes a new energy power plant, a sending-end flexible DC converter station, a receiving-end flexible DC converter station, a DC overhead line, and an AC energy-consuming device. The new energy power plant is commonly connected to the sending-end flexible DC converter station through a three-phase AC bus. The AC energy-consuming device is connected between the new energy power plant and the sending-end flexible DC converter station. The sending-end flexible DC converter station is connected to the receiving-end flexible DC converter station through a bipolar DC overhead line. The sending-end flexible DC converter station, the DC overhead line, and the receiving-end flexible DC converter station form a true bipolar DC system;

[0007] S2. Configure the control strategies for the sending-end flexible DC converter station and the receiving-end flexible DC converter station. Among them, all sending-end flexible DC converter stations adopt a double-closed-loop control strategy of constant AC voltage and frequency. Only one receiving-end flexible DC converter station adopts a constant DC voltage control strategy, and the remaining receiving-end flexible DC converter stations adopt a constant active power control strategy;

[0008] S3. Each sending-end flexible DC converter station and receiving-end flexible DC converter station real-time detect the DC voltage and current, and judge whether a DC fault occurs in the line according to the DC voltage and current. If so, simultaneously execute Step S6 and Step S7;

[0009] S4. Each pole of the sending-end flexible DC converter station real-time detects the DC current flowing out of this pole. If it detects that the DC current flowing out of this pole increases, then this pole automatically reduces the DC voltage offset through the DC controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, and outputs a negative DC voltage to actively eliminate the DC fault;

[0010] S5. Each pole of the receiving-end flexible DC converter station real-time detects the DC current flowing into this pole. If it detects that the DC current flowing into this pole decreases and reversely increases, then this pole automatically reduces the DC voltage offset through the DC current controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, and outputs a negative DC voltage to actively eliminate the DC fault;

[0011] S6. After detecting a DC fault, the control systems of each sending-end flexible DC converter station and receiving-end flexible DC converter station enter the deionization logic. Each sending-end flexible DC converter station and receiving-end flexible DC converter station set the DC current reference value input to the DC current controller of the faulty pole to zero for zero DC current control. At the same time, each sending-end flexible DC converter station and receiving-end flexible DC converter station set the active current command input to the outer loop controller of the faulty pole to zero;

[0012] S7. After detecting a DC fault, judge whether the true bipolar DC system is in bipolar operation. If so, execute Step S8. If not, execute Step S9;

[0013] S8. Transfer the power of the faulty pole to the non-faulty pole. If there is still power surplus at the sending end, calculate the number of AC energy-consuming device groups to be put into operation according to the first preset formula, and put into the corresponding number of AC energy-consuming device groups. The first preset formula is:

[0014] P 送端正常极剩余容量 = P 额定功率 - P 送端正常极

[0015]

[0016] where P 送端正常极剩余容量 is the remaining capacity of the normal pole of the sending-end flexible DC converter station, P 额定功率 is the rated power of the sending-end flexible DC converter station, P 送端正常极 is the active power of the normal pole of the sending-end flexible DC converter station, N 交流耗能装置组数 is the number of AC energy-consuming device groups to be put into operation, P 送端双极功率 is the bipolar operating active power of the sending-end flexible DC converter station, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices;

[0017] S9. Calculate the number of AC energy-consuming device groups to be put into operation according to the second preset formula, and put into the corresponding number of AC energy-consuming device groups. The second preset formula is:

[0018]

[0019] where N 交流耗能装置组数 is the number of AC energy-consuming device groups to be put into operation, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices;

[0020] S10. When each sending-end flexible DC converter station and receiving-end flexible DC converter station detect that the DC voltage has recovered to the preset value, the sending-end flexible DC converter station removes the AC energy-consuming device groups one by one, restores the DC current, and completes the restart of the DC fault.

[0021] Optionally, before step S10, it further includes:

[0022] S010. When the deionization time is reached, each sending-end flexible DC converter station and receiving-end flexible DC converter station restore the slope of the DC reference value input to the DC power controller of the faulty pole, and each sending-end flexible DC converter station and receiving-end flexible DC converter station cut back the active current command of the faulty pole to be controlled by the outer-loop controller to restore the DC voltage.

[0023] Optionally, the deionization time is 30 ms - 400 ms.

[0024] Optionally, the new energy power grid includes a wind farm and a photovoltaic power grid.

[0025] Optionally, the number of sending - end flexible DC converter stations is one or more than two, and the number of receiving - end flexible DC converter stations is one or more than two.

[0026] The second aspect of the present invention provides a new energy island power grid transmission system, including a new energy power grid, a sending - end flexible DC converter station, a receiving - end flexible DC converter station, a DC overhead line, and an AC energy - consuming device. The new energy power grid is commonly connected to the sending - end flexible DC converter station through a three - phase AC bus. The AC energy - consuming device is connected between the new energy power grid and the sending - end flexible DC converter station. The sending - end flexible DC converter station is connected to the receiving - end flexible DC converter station through a bipolar DC overhead line. The sending - end flexible DC converter station, the DC overhead line, and the receiving - end flexible DC converter station form a true bipolar DC system;

[0027] All sending - end flexible DC converter stations adopt a double - closed - loop control strategy of constant AC voltage and frequency. Only one of the receiving - end flexible DC converter stations adopts a constant DC voltage control strategy, and the remaining receiving - end flexible DC converter stations adopt a constant active power control strategy;

[0028] When the new energy island power grid transmission system is operating, each sending - end flexible DC converter station and receiving - end flexible DC converter station detect the DC voltage and current in real - time, and judge whether a DC fault occurs in the line according to the DC voltage and current. If so, steps A1 and B1 are executed simultaneously;

[0029] When the new energy island power grid transmission system is operating, each pole of the sending - end flexible DC converter station detects the DC current flowing out of this pole in real - time. If it is detected that the DC current flowing out of this pole increases, this pole automatically reduces the DC voltage offset through a DC controller, reduces the number of arm sub - modules input on the DC side, directly controls the DC voltage, and outputs a negative DC voltage to actively clear the DC fault;

[0030] When the new energy island power grid transmission system is operating, each pole of the receiving - end flexible DC converter station detects the DC current flowing into this pole in real - time. If it is detected that the DC current flowing into this pole decreases and reversely increases, this pole automatically reduces the DC voltage offset through a DC current controller, reduces the number of arm sub - modules input on the DC side, directly controls the DC voltage, and outputs a negative DC voltage to actively clear the DC fault;

[0031] A1. After a DC fault is detected, the control systems of each sending-end Flexible DC converter station and receiving-end Flexible DC converter station enter the de-ionization logic. Each sending-end Flexible DC converter station and receiving-end Flexible DC converter station resets the DC current reference value input to the DC current controller of the faulty pole to zero, performing zero DC current control. Simultaneously, each sending-end Flexible DC converter station and receiving-end Flexible DC converter station resets the active current command input to the outer loop controller of the faulty pole to zero.

[0032] B1. After detecting a DC fault, determine whether the true bipolar DC system is in bipolar operation. If so, execute step B2; if not, execute step B3.

[0033] B2. Transfer the power from the faulty pole to the non-faulty pole. If there is still power surplus at the sending end, calculate the number of AC energy consuming device groups to be put into operation according to the first preset formula, and put into operation the corresponding number of AC energy consuming device groups. The first preset formula is:

[0034] P 送端正常极剩余容量 =P 额定功率 -P 送端正常极

[0035]

[0036] Among them, P 送端正常极剩余容量 is the normal pole residual capacity of the sending-end flexible DC converter station, P 额定功率 is the rated power of the sending-end flexible DC converter station, P 送端正常极 is the normal active power of the sending-end flexible DC converter station, N 交流耗能装置组数 P is the number of AC energy-consuming device groups to be invested, 送端双极功率 is the bipolar operating active power of the sending-end flexible DC converter station, P 送端故障极 is the fault pole active power of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy consuming devices;

[0037] B3. Calculate the number of AC energy consuming device groups to be put into operation according to the second preset formula, and put into operation a corresponding number of AC energy consuming device groups. The second preset formula is:

[0038]

[0039] Among them, N 交流耗能装置组数 P is the number of AC energy-consuming device groups to be invested, 送端故障极 is the fault pole active power of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy consuming devices;

[0040] After each sending - end flexible DC converter station and receiving - end flexible DC converter station in the new - energy island power grid transmission system detect that the DC voltage has recovered to the preset value, the sending - end flexible DC converter station cuts off the AC energy - consuming devices in groups, restores the DC current, and completes the restart of the DC fault.

[0041] Optionally, before each sending - end flexible DC converter station and receiving - end flexible DC converter station in the new - energy island power grid transmission system detect that the DC voltage has recovered to the preset value, the sending - end flexible DC converter station cuts off the AC energy - consuming devices in groups, restores the DC current, and completes the restart of the DC fault, the new - energy island power grid transmission system also performs the following operations:

[0042] When the de - ionization time is reached, each sending - end flexible DC converter station and receiving - end flexible DC converter station restore the slope of the DC reference value input to the DC power controller of the faulty pole, and each sending - end flexible DC converter station and receiving - end flexible DC converter station cut back the active current command of the faulty pole to be controlled by the outer - loop controller to restore the DC voltage.

[0043] Optionally, the de - ionization time is 300 ms to 400 ms.

[0044] Optionally, the new - energy power field includes a wind farm and a photovoltaic power field.

[0045] Optionally, the number of sending - end flexible DC converter stations is one or more than two, and the number of receiving - end flexible DC converter stations is one or more than two.

[0046] From the above technical solutions, it can be seen that the DC - fault self - clearing method for the new - energy island power grid transmission system and the new - energy island power grid transmission system provided by the present invention have the following advantages:

[0047] The DC fault self-clearing method for the new energy island power grid transmission system provided by the present invention adopts a true bipolar DC system. The bipolar operation greatly improves the stable operation ability of the DC transmission system. Even after a single-pole fault and even ultimate blocking, the stable operation of the sending-end island system can still be maintained by the normal pole. The sending end adopts a constant AC voltage and frequency control strategy to provide the required AC voltage and frequency for each new energy power station. There is only one receiving end that adopts a constant DC voltage control strategy to provide a stable DC voltage for the DC system, and the remaining receiving ends adopt a constant active power control strategy. At the same time, each pole of the sending-end flexible DC converter station detects the DC current flowing out of this pole in real time, and each pole of the receiving-end flexible DC converter station detects the DC current flowing into this pole in real time. If each pole of the sending-end flexible DC converter station detects that the DC current flowing into this pole decreases and then increases in the reverse direction, this pole automatically reduces the DC voltage offset amount through the DC current controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault. If each pole of the receiving-end flexible DC converter station detects that the DC current flowing into this pole decreases and then increases in the reverse direction, this pole automatically reduces the DC voltage offset amount through the DC current controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault. For the control strategies of the sending end and the receiving end, after detecting a DC fault, the control systems of each sending-end flexible DC converter station and receiving-end flexible DC converter station enter the deionization logic. Each sending-end flexible DC converter station and receiving-end flexible DC converter station set the DC current reference value input to the DC current controller of the faulty pole to zero for zero DC current control. At the same time, each sending-end flexible DC converter station and receiving-end flexible DC converter station set the active current command input to the outer-loop controller of the faulty pole to zero. At the same time, it is judged whether the true bipolar DC system is operating in a bipolar mode. If so, the power of the faulty pole is transferred to the non-faulty pole. If there is still power surplus at the sending end, the number of AC energy-consuming device groups to be put into operation is calculated according to the first preset formula, and the corresponding number of AC energy-consuming device groups is put into operation. Otherwise, the number of AC energy-consuming device groups to be put into operation is calculated according to the second preset formula, and the corresponding number of AC energy-consuming device groups is put into operation. When each sending-end flexible DC converter station and receiving-end flexible DC converter station detects that the DC voltage has recovered to the preset value, the sending-end flexible DC converter station removes the AC energy-consuming device groups one by one, restores the DC current, and completes the restart of the DC fault., after the receiving - end converter detects the occurrence of a DC fault, it automatically clears the DC fault according to its respective control strategies, and cooperates with the sending - end AC energy consumption to achieve the energy balance of the sending - end island, improving the power regulation ability and system stability of the new - energy island power grid transmission system. During the DC fault clearing period, there is no need to actively control the fault current through a negative - voltage output strategy, reducing the control difficulty and solving the technical problems of the DC fault - ride - through technology of the new - energy island power grid transmission system. At the moment of DC fault, the new - energy power regulation ability is weak, it is difficult to quickly solve the problem of energy imbalance between the AC and DC sides, and it is difficult to extinguish the arc within the set de - ionization time, affecting system stability. Moreover, during the DC fault clearing period, it is necessary to actively control the fault current through a negative - voltage output strategy, resulting in a large control difficulty.

[0048] The new - energy island power grid transmission system provided by the present invention is used to execute the DC fault self - clearing method of the new - energy island power grid transmission system provided by the present invention. Its principle and the achieved technical effects are the same as those of the DC fault self - clearing method of the new - energy island power grid transmission system provided by the present invention, and will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other relevant drawings can also be obtained based on these drawings.

[0050] Figure 1 It is a schematic flow chart of a DC fault self - clearing method for a new - energy island power grid transmission system provided in an embodiment of the present invention;

[0051] Figure 2 It is a schematic structural diagram of a new - energy island power grid transmission system provided in an embodiment of the present invention;

[0052] Figure 3 It is a schematic diagram of the control strategy of the receiving - end flexible DC converter station of the new - energy island power grid transmission system provided in an embodiment of the present invention;

[0053] Figure 4 It is a schematic diagram of the control strategy of the sending - end flexible DC converter station of the new - energy island power grid transmission system provided in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] To enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solution in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0055] For ease of understanding, please refer to Figure 1 , an embodiment of a method for self-clearing DC faults in a new energy island power grid transmission system provided in the present invention includes:

[0056] Step 101: Build a new energy island power grid transmission system, which includes a new energy power plant, a sending-end flexible DC converter station, a receiving-end flexible DC converter station, a DC overhead line, and an AC energy-consuming device. The new energy power plant is commonly connected to the sending-end flexible DC converter station through a three-phase AC bus. The AC energy-consuming device is connected between the new energy power plant and the sending-end flexible DC converter station. The sending-end flexible DC converter station is connected to the receiving-end flexible DC converter station through a bipolar DC overhead line, and the sending-end flexible DC converter station, the DC overhead line, and the receiving-end flexible DC converter station form a true bipolar DC system.

[0057] It should be noted that in the embodiments of the present invention, first, a new energy island power grid transmission system is established. The architecture of the new energy island power grid transmission system is as Figure 2 shown, including a new energy power plant, a sending-end flexible DC converter station, a receiving-end flexible DC converter station, a DC overhead line, and an AC energy-consuming device. The new energy power plant is commonly connected to the sending-end flexible DC converter station through a three-phase AC bus. The AC energy-consuming device is connected between the new energy power plant and the sending-end flexible DC converter station. The sending-end flexible DC converter station is connected to the receiving-end flexible DC converter station through a bipolar DC overhead line, and the sending-end flexible DC converter station, the DC overhead line, and the receiving-end flexible DC converter station form a true bipolar DC system. The new energy power plant includes renewable energy power plants such as a wind farm and a photovoltaic power plant. The AC energy-consuming device is used to dissipate the continuous active power output of the new energy power plant when the active power transmission channel of the DC line is blocked, and avoid overvoltage problems caused by energy accumulation in the sending-end AC feeder.

[0058] The sending-end flexible DC converter station and the receiving-end flexible DC converter station can adopt a single valve group form or a double valve group series form. The converter valves can use full-bridge sub-modules or a combination of full-bridge sub-modules and half-bridge sub-modules. The flexible DC converter station consists of three-phase six-arm bridges, with each phase containing upper and lower arms. Each arm is composed of N sub-modules connected in series with an arm reactor. Each arm is composed of the same number of sub-module converter valves. For example, when the DC voltage is 400 kV, the number of sub-modules in each arm is 200, and the capacitor voltage of each sub-module is 2 kV. The number of sending-end flexible DC converter stations can be one or more to achieve single-source or multi-source power supply. The number of receiving-end flexible DC converter stations can be one or more to achieve single-drop or multi-drop power reception. If there are multiple sending-end or multiple receiving-end flexible DC converter stations, the DC overhead lines mainly connect the DC sides of each converter station. The connection method can be star connection or delta connection. The sending-end flexible DC converter station, the DC overhead lines, and the receiving-end flexible DC converter station form a true bipolar DC system. The bipolar is completely symmetric, and bipolar operation greatly improves the stable operation ability of the DC transmission system. The grounding method is simple, and even after a single-pole fault and subsequent final blocking, the normal pole can still maintain the stable operation of the sending-end island system.

[0059] Step 102: Configure the control strategies for the sending-end flexible DC converter station and the receiving-end flexible DC converter station. Among them, all sending-end flexible DC converter stations adopt a double-closed-loop control strategy of constant AC voltage and frequency. There is exactly one receiving-end flexible DC converter station that adopts a constant DC voltage control strategy, and the remaining receiving-end flexible DC converter stations adopt a constant active power control strategy.

[0060] It should be noted that when configuring the control strategies for the sending-end flexible DC converter station and the receiving-end flexible DC converter station, the sending-end all adopts a double-closed-loop control strategy of constant AC voltage and frequency to provide the AC voltage and frequency required for the operation of their respective new energy power plants. There is exactly one receiving-end flexible DC converter station that adopts a constant DC voltage control strategy to provide a stable DC voltage for the DC system, and the remaining receiving-end flexible DC converter stations adopt a constant active power control strategy. As Figure 3 and Figure 4 shown, Figure 3 Figure 12 is a schematic diagram of the control strategy for the receiving-end flexible DC converter station, Figure 4 and Figure 14 is a schematic diagram of the control strategy for the sending-end flexible DC converter station.

[0061] Step 103: Each sending-end flexible DC converter station and receiving-end flexible DC converter station continuously detect the DC voltage and current, and judge whether a DC fault has occurred in the line based on the DC voltage and current. If so, then simultaneously execute Step 106 and Step 107.

[0062] It should be noted that after the control strategy is configured, each sending-end flexible DC converter station and receiving-end flexible DC converter station detect the DC voltage and current in real time. In DC projects, line protections such as traveling wave protection or sudden change protection are often used to detect whether a DC fault has occurred in the line. The detection method of DC faults is an existing technology, and the specific implementation process will not be elaborated here. If a DC fault is detected in the line, then steps 106 and 107 are executed simultaneously; otherwise, the DC fault detection of the line continues.

[0063] Step 104: Each pole of the sending-end flexible DC converter station detects the DC current flowing out of this pole in real time. If it is detected that the DC current flowing out of this pole increases, then this pole automatically reduces the DC voltage offset through the DC controller, reduces the number of arm sub-modules put into the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault.

[0064] Step 105: Each pole of the receiving-end flexible DC converter station detects the DC current flowing into this pole in real time. If it is detected that the DC current flowing into this pole decreases and then increases in the reverse direction, then this pole automatically reduces the DC voltage offset through the DC current controller, reduces the number of arm sub-modules put into the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault.

[0065] It should be noted that while step 103 is being executed, each pole of the sending-end flexible DC converter station detects the DC current flowing out of this pole in real time, and each pole of the receiving-end flexible DC converter station detects the DC current flowing into this pole in real time. If the sending-end flexible DC converter station detects that the DC current flowing out of a certain pole increases, then this pole of the sending-end flexible DC converter station automatically reduces the DC voltage offset through the DC current controller, reduces the number of arm sub-modules put into the DC side, realizes direct control of the DC voltage, outputs a negative DC voltage, and actively clears the DC fault. This process is a completely automatic control, does not rely on the detection of faults by DC protection, can quickly clear DC faults, and can effectively avoid being affected by misoperation or refusal to operate of the protection at the same time. If the receiving-end flexible DC converter station detects that the DC current flowing into a certain pole decreases and then increases in the reverse direction, then this pole of the receiving-end flexible DC converter station automatically reduces the DC voltage offset through the DC current controller, reduces the number of sub-modules put into the DC side, realizes direct control of the DC voltage, outputs a negative DC voltage, and actively clears the DC fault. This process is a completely automatic control, does not rely on the detection of faults by DC protection, can quickly clear DC faults, and can effectively avoid being affected by misoperation or refusal to operate of the protection at the same time.

[0066] Such as Figure 3 and Figure 4As shown in the figure, the DC current controller utilizes the characteristic that the full-bridge sub-module can output negative voltage, and adopts a control method based on the DC current margin. It compares the DC current command with the actual DC current. When a DC overhead line ground fault occurs, for the sending-end flexible DC converter station, its DC current increases rapidly. Therefore, the output of the DC current controller decreases rapidly, and even becomes negative, quickly reducing the actual DC voltage to automatically clear the DC fault. For the receiving-end flexible DC converter station, its DC current will inevitably go through a process from decreasing to increasing in the reverse direction. The output of the DC current controller also decreases rapidly, and even becomes negative, quickly reducing the actual DC voltage to actively clear the DC fault.

[0067] As Figure 3 and Figure 4 shown in the figure, the outer-loop control of the sending-end flexible DC converter station and the receiving-end flexible DC converter station includes active power control (active power control, DC voltage control, frequency control) and reactive power control (reactive power control, AC voltage control). When the flexible DC converter station (i.e., the sending-end flexible DC converter station) is used to connect renewable energy to the grid, a double-closed-loop control strategy of constant AC voltage and frequency is adopted. As Figure 4 shown in the figure, it provides AC voltage support for the sending-end island power grid. The inner-loop control includes active current control and reactive current control. The inner-loop control link receives the reference values of active and reactive currents from the outer-loop control and quickly tracks the reference current to achieve direct control of the voltage amplitude and phase on the AC side of the valve group.

[0068] Step 106: After detecting a DC fault, the control systems of each sending-end flexible DC converter station and receiving-end flexible DC converter station enter the deionization logic. Each sending-end flexible DC converter station and receiving-end flexible DC converter station set the DC current reference value input to the DC current controller of the faulty pole to zero for zero DC current control. At the same time, each sending-end flexible DC converter station and receiving-end flexible DC converter station set the active current command input to the outer-loop controller of the faulty pole to zero.

[0069] It should be noted that after the DC protection device detects a DC fault, the control systems of each converter station enter the deionization logic (when charged protons (electrons, ions) neutralize and disappear with each other, it is called deionization). Each sending-end flexible DC converter station and receiving-end flexible DC converter station set the DC current reference value input to the DC current controller of the faulty pole to zero for zero DC current control to assist in quickly extinguishing the DC current arc and deionization. At the same time, both the sending-end flexible DC converter station and the receiving-end converter station need to set the active current command output by the outer-loop controller of the faulty pole to avoid continuous charging of the capacitor of the faulty pole sub-module on the AC side during the DC fault.

[0070] Step 107: After detecting a DC fault, determine whether the true bipolar DC system is operating in bipolar mode. If so, execute Step 108; if not, execute Step 109.

[0071] It should be noted that when a DC fault is detected, it is necessary to determine whether the DC system is operating in bipolar mode. For the cases of bipolar operation and monopolar operation, different processing methods are used to balance the sending-end energy and maintain the stable operation of the sending-end island system. Specifically, as described in Step 108 and Step 109.

[0072] Step 108: Transfer the power of the faulty pole to the non-faulty pole. If there is still power surplus at the sending end, calculate the number of AC energy-consuming device groups to be put into operation according to the first preset formula, and put into operation the corresponding number of AC energy-consuming device groups. The first preset formula is:

[0073] P 送端正常极剩余容量 =P 额定功率 -P 送端正常极

[0074]

[0075] where, P 送端正常极剩余容量 is the remaining capacity of the normal pole of the sending-end flexible DC converter station, P 额定功率 is the rated power of the sending-end flexible DC converter station, P 送端正常极 is the active power of the normal pole of the sending-end flexible DC converter station, N 交流耗能装置组数 is the number of AC energy-consuming device groups to be put into operation, P 送端双极功率 is the active power of the bipolar operation of the sending-end flexible DC converter station, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices.

[0076] Step 109: Calculate the number of AC energy-consuming device groups to be put into operation according to the second preset formula, and put into operation the corresponding number of AC energy-consuming device groups. The second preset formula is:

[0077]

[0078] where, N 交流耗能装置组数 is the number of AC energy-consuming device groups to be put into operation, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices.

[0079] Step 110: When each sending-end flexible DC converter station and receiving-end flexible DC converter station detect that the DC voltage has recovered to the preset value, the sending-end flexible DC converter station removes the AC energy-consuming devices group by group, restores the DC current, and completes the restart of the DC fault.

[0080] It should be noted that when each sending-end flexible DC converter station and receiving-end flexible DC converter station detect that the DC voltage has recovered to the preset value, that is, the system stable operation value, the sending-end flexible DC converter station cuts off the AC energy-consuming devices in groups, restores the DC current, and completes the restart of the DC fault.

[0081] The DC fault self-clearing method for the new energy island power grid transmission system provided by the embodiments of the present invention adopts a true bipolar DC system. The bipolar operation greatly improves the stable operation ability of the DC transmission system. Even after a single-pole fault and even ultimate blocking, the normal pole can still maintain the stable operation of the sending-end island system. The sending end adopts a fixed AC voltage and frequency control strategy to provide the required AC voltage and frequency for each new energy power station. There is only one receiving end that adopts a fixed DC voltage control strategy to provide a stable DC voltage for the DC system, and the remaining receiving ends adopt a fixed active power control strategy. At the same time, each pole of the sending-end flexible DC converter station detects the DC current flowing out of this pole in real time, and each pole of the receiving-end flexible DC converter station detects the DC current flowing into this pole in real time. If each pole of the sending-end flexible DC converter station detects that the DC current flowing into this pole decreases and then increases in the reverse direction, this pole automatically reduces the DC voltage offset through the DC current controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault. If each pole of the receiving-end flexible DC converter station detects that the DC current flowing into this pole decreases and then increases in the reverse direction, this pole automatically reduces the DC voltage offset through the DC current controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault. For the control strategies of the sending end and the receiving end, after detecting a DC fault, the control systems of each sending-end flexible DC converter station and receiving-end flexible DC converter station enter the deionization logic. Each sending-end flexible DC converter station and receiving-end flexible DC converter station set the DC current reference value input to the DC current controller of the faulty pole to zero for zero DC current control. At the same time, each sending-end flexible DC converter station and receiving-end flexible DC converter station set the active current command input to the outer-loop controller of the faulty pole to zero. At the same time, it is judged whether the true bipolar DC system is in bipolar operation. If so, the power of the faulty pole is transferred to the non-faulty pole. If there is still power surplus at the sending end, the number of groups of AC energy-consuming device groups to be input is calculated according to the first preset formula, and the corresponding number of AC energy-consuming device groups is input. Otherwise, the number of groups of AC energy-consuming device groups to be input is calculated according to the second preset formula, and the corresponding number of AC energy-consuming device groups is input. When each sending-end flexible DC converter station and receiving-end flexible DC converter station detect that the DC voltage has recovered to the preset value, the sending-end flexible DC converter station cuts off the AC energy-consuming device groups one by one, restores the DC current, and completes the restart of the DC fault.It improves the power regulation ability and system stability of the new - energy island power grid transmission system. During the DC fault clearing period, it is not necessary to actively control the fault current through a negative - voltage output strategy, reducing the control difficulty. It can be applied to the long - distance and high - power new - energy transmission scenarios, solving the technical problems of the DC fault - ride - through technology of the new - energy island power grid transmission system. At the moment of DC fault, the new - energy power regulation ability is weak, it is difficult to quickly solve the AC - DC side energy imbalance problem, and it is difficult to extinguish the arc within the set deionization time, affecting system stability. Moreover, during the DC fault clearing period, it is necessary to actively control the fault current through a negative - voltage output strategy, with a large control difficulty.

[0082] In one embodiment, before step 110, when the deionization time (the deionization time in the embodiments of the present invention is 300 ms - 400 ms) is reached, each sending - end flexible DC converter station and receiving - end flexible DC converter station restore the slope of the DC reference value input to the DC power controller of the faulty pole (which is an adjustable value), and each sending - end flexible DC converter station and receiving - end flexible DC converter station switch the active - current command of the faulty pole back to be controlled by the outer - loop controller to restore the DC voltage.

[0083] For ease of understanding, please refer to Figures 2 to 4 , an embodiment of a new - energy island power grid transmission system is provided in the present invention, including a new - energy power plant, a sending - end flexible DC converter station, a receiving - end flexible DC converter station, a DC overhead line, and an AC energy - consuming device. The new - energy power plant is commonly connected to the sending - end flexible DC converter station through a three - phase AC bus. The AC energy - consuming device is connected between the new - energy power plant and the sending - end flexible DC converter station. The sending - end flexible DC converter station is connected to the receiving - end flexible DC converter station through a bipolar DC overhead line. The sending - end flexible DC converter station, the DC overhead line, and the receiving - end flexible DC converter station form a true - bipolar DC system;

[0084] All sending - end flexible DC converter stations adopt a double - closed - loop constant - AC - voltage and frequency control strategy. Only one receiving - end flexible DC converter station adopts a constant - DC - voltage control strategy, and the remaining receiving - end flexible DC converter stations adopt a constant - active - power control strategy;

[0085] When the new - energy island power grid transmission system is operating, each sending - end flexible DC converter station and receiving - end flexible DC converter station detect the DC voltage and current in real - time, and judge whether a DC fault occurs in the line according to the DC voltage and current. If so, step A1 and step B1 are executed simultaneously;

[0086] When the new energy island power grid sending system is in operation, each pole of the sending-end flexible DC converter station detects the DC current flowing out of this pole in real time. If it detects that the DC current flowing out of this pole increases, this pole automatically reduces the DC voltage offset through the DC controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault;

[0087] When the new energy island power grid sending system is in operation, each pole of the receiving-end flexible DC converter station detects the DC current flowing into this pole in real time. If it detects that the DC current flowing into this pole decreases and reversely increases, this pole automatically reduces the DC voltage offset through the DC current controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault;

[0088] A1. After detecting a DC fault, the control systems of each sending-end flexible DC converter station and receiving-end flexible DC converter station enter the deionization logic. Each sending-end flexible DC converter station and receiving-end flexible DC converter station set the DC current reference value input to the DC current controller of the faulty pole to zero, perform zero DC current control, and at the same time, each sending-end flexible DC converter station and receiving-end flexible DC converter station set the active current command input to the outer-loop controller of the faulty pole to zero;

[0089] B1. After detecting a DC fault, determine whether the true bipolar DC system is operating in bipolar mode. If it is, execute step B2; if not, execute step B3;

[0090] B2. Transfer the power of the faulty pole to the non-faulty pole. If there is still power surplus at the sending end, calculate the number of AC energy-consuming device groups to be put into operation according to the first preset formula, and put into the corresponding number of AC energy-consuming device groups. The first preset formula is:

[0091] P 送端正常极剩余容量 =P 额定功率 -P 送端正常极

[0092]

[0093] where P 送端正常极剩余容量 is the remaining capacity of the normal pole of the sending-end flexible DC converter station, P 额定功率 is the rated power of the sending-end flexible DC converter station, P 送端正常极 is the active power of the normal pole of the sending-end flexible DC converter station, N 交流耗能装置组数 is the number of AC energy-consuming device groups to be put into operation, P 送端双极功率 is the active power of the bipolar operation of the sending-end flexible DC converter station, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices;

[0094] B3. Calculate the number of AC energy-consuming device groups to be put into operation according to the second preset formula, and put into the corresponding number of AC energy-consuming device groups. The second preset formula is:

[0095]

[0096] where N 交流耗能装置组数 is the number of AC energy-consuming device groups to be put into operation, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, and P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices;

[0097] After the DC voltage at each sending-end flexible DC converter station and receiving-end flexible DC converter station in the new energy island power grid sending system is detected to have recovered to the preset value, the sending-end flexible DC converter station removes the AC energy-consuming device groups one by one, restores the DC current, and completes the restart of the DC fault.

[0098] Before the sending-end flexible DC converter station removes the AC energy-consuming device groups one by one, restores the DC current, and completes the restart of the DC fault after the DC voltage at each sending-end flexible DC converter station and receiving-end flexible DC converter station in the new energy island power grid sending system is detected to have recovered to the preset value, the new energy island power grid sending system also performs the following operations:

[0099] When the deionization time is reached, the DC reference value slope input to the DC power controller of the faulty pole at each sending-end flexible DC converter station and receiving-end flexible DC converter station is restored, and the active current command of the faulty pole at each sending-end flexible DC converter station and receiving-end flexible DC converter station is switched back to be controlled by the outer-loop controller to restore the DC voltage.

[0100] The deionization time is 300 ms to 400 ms.

[0101] The new energy power plant includes a wind farm and a photovoltaic power plant.

[0102] The number of sending-end flexible DC converter stations is one or more than two, and the number of receiving-end flexible DC converter stations is one or more than two.

[0103] The new energy island power grid transmission system provided by the embodiments of the present invention adopts a true bipolar DC system. The bipolar operation greatly improves the stable operation ability of the DC transmission system. Even after a single-pole fault and even final blocking, the normal pole can still maintain the stable operation of the sending-end island system. The sending end adopts a constant AC voltage and frequency control strategy to provide the AC voltage and frequency required for the operation of each new energy power plant. There is only one receiving end that adopts a constant DC voltage control strategy to provide a stable DC voltage for the DC system, and the remaining receiving ends adopt a constant active power control strategy. At the same time, each pole of the sending-end flexible DC converter station detects the DC current flowing out of this pole in real time, and each pole of the receiving-end flexible DC converter station detects the DC current flowing into this pole in real time. If each pole of the sending-end flexible DC converter station detects that the DC current flowing into this pole decreases and reversely increases, then this pole automatically reduces the DC voltage offset amount through the DC current controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault. If each pole of the receiving-end flexible DC converter station detects that the DC current flowing into this pole decreases and reversely increases, then this pole automatically reduces the DC voltage offset amount through the DC current controller, reduces the number of arm sub-modules input on the DC side, directly controls the DC voltage, outputs a negative DC voltage, and actively clears the DC fault. For the control strategies of the sending end and the receiving end, after detecting a DC fault, the control systems of each sending-end flexible DC converter station and receiving-end flexible DC converter station enter the deionization logic. Each sending-end flexible DC converter station and receiving-end flexible DC converter station set the DC current reference value input to the DC current controller of the faulty pole to zero for zero DC current control. At the same time, each sending-end flexible DC converter station and receiving-end flexible DC converter station set the active current command input to the outer-loop controller of the faulty pole to zero. At the same time, it is judged whether the true bipolar DC system is operating in bipolar mode. If so, the power of the faulty pole is transferred to the non-faulty pole. If there is still power surplus at the sending end, the number of AC energy-consuming device groups to be put into operation is calculated according to the first preset formula, and the corresponding number of AC energy-consuming device groups is put into operation. Otherwise, the number of AC energy-consuming device groups to be put into operation is calculated according to the second preset formula, and the corresponding number of AC energy-consuming device groups is put into operation. When each sending-end flexible DC converter station and receiving-end flexible DC converter station detects that the DC voltage has recovered to the preset value, the sending-end flexible DC converter station removes the AC energy-consuming device groups one by one, restores the DC current, and completes the restart of the DC fault., after detecting the occurrence of a DC fault, the receiving-end converter automatically clears the DC fault according to its respective control strategies, and cooperates with the sending-end AC energy consumption to achieve the energy balance of the sending-end island, improving the power regulation ability and system stability of the new energy island power grid sending system. During the DC fault clearing period, there is no need to actively control the fault current through the negative voltage output strategy, reducing the control difficulty. It can be applied to the long-distance and high-power new energy transmission scenarios, solving the technical problems that in the DC fault crossing technology of the new energy island power grid sending system, the new energy power regulation ability is weak at the moment of DC fault, it is difficult to quickly solve the energy imbalance problem between the AC and DC sides, and it is difficult to extinguish the arc within the set deionization time, affecting the system stability, and during the DC fault clearing period, it is necessary to actively control the fault current through the negative voltage output strategy, resulting in a large control difficulty.

[0104] The new energy island power grid sending system provided in the embodiments of the present invention is used to execute the DC fault self-clearing method in the embodiments of the DC fault self-clearing method of the new energy island power grid sending system provided by the present invention. Its principle and the obtained technical effects are the same as those of the DC fault self-clearing method of the new energy island power grid sending system provided in the embodiments of the present invention, and will not be elaborated here.

[0105] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A DC fault self-clearing method for a new energy island power grid transmission system, characterized in that, Including: S1. Build a power transmission system for a new energy island power grid. The power transmission system for the new energy island power grid includes a new energy power plant, a sending-end flexible DC converter station, a receiving-end flexible DC converter station, a DC overhead line, and an AC energy-consuming device. The new energy power plant is commonly connected to the sending-end flexible DC converter station through a three-phase AC bus. The AC energy-consuming device is connected between the new energy power plant and the sending-end flexible DC converter station. The sending-end flexible DC converter station is connected to the receiving-end flexible DC converter station through a bipolar DC overhead line. The sending-end flexible DC converter station, the DC overhead line, and the receiving-end flexible DC converter station form a true bipolar DC system. S2. Configure the control strategies for the sending-end flexible DC converter station and the receiving-end flexible DC converter station. Among them, all sending-end flexible DC converter stations adopt a double-closed-loop constant AC voltage and frequency control strategy. There is exactly one receiving-end flexible DC converter station that adopts a constant DC voltage control strategy, and the remaining receiving-end flexible DC converter stations adopt a constant active power control strategy. S3. Each sending-end flexible DC converter station and receiving-end flexible DC converter station detect the DC voltage and current in real time, and judge whether a DC fault occurs in the line according to the DC voltage and current. If so, perform step S6 and step S7 simultaneously. S4. Each pole of the sending-end flexible DC converter station detects the DC current flowing out of this pole in real time. If it detects that the DC current flowing out of this pole increases, then this pole automatically reduces the DC voltage offset through the DC controller, reduces the number of arm sub-modules put into the DC side, directly controls the DC voltage, and outputs a negative DC voltage to actively eliminate the DC fault. S5. Each pole of the receiving-end flexible DC converter station detects the DC current flowing into this pole in real time. If it detects that the DC current flowing into this pole decreases and increases in the reverse direction, then this pole automatically reduces the DC voltage offset through the DC current controller, reduces the number of arm sub-modules put into the DC side, directly controls the DC voltage, and outputs a negative DC voltage to actively eliminate the DC fault. S6. After detecting a DC fault, the control systems of each sending-end flexible DC converter station and receiving-end flexible DC converter station enter the deionization logic. Each sending-end flexible DC converter station and receiving-end flexible DC converter station set the DC current reference value input to the DC current controller of the faulty pole to zero for zero DC current control. At the same time, each sending-end flexible DC converter station and receiving-end flexible DC converter station set the active current command input to the outer-loop controller of the faulty pole to zero. S7. After detecting a DC fault, judge whether the true bipolar DC system is in bipolar operation. If so, perform step S8. If not, perform step S9. S8. Transfer the power of the faulty pole to the non-faulty pole. If there is still power surplus at the sending end, calculate the number of groups of AC energy-consuming devices to be put into operation according to the first preset formula, and put into the corresponding number of groups of AC energy-consuming devices. The first preset formula is: P 送端正常极剩余容量 = P 额定功率 -P 送端正常极 Among them, P 送端正常极剩余容量 is the remaining capacity of the normal pole of the sending-end flexible DC converter station, P 额定功率 is the rated power of the sending-end flexible DC converter station, P 送端正常极 is the active power of the normal pole of the sending-end flexible DC converter station, N 交流耗能装置组数 is the number of AC energy-consuming device groups to be put into operation, P 送端双极功率 is the active power of the bipolar operation of the sending-end flexible DC converter station, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices; S9. Calculate the number of groups of AC energy-consuming devices to be put into operation according to the second preset formula, and put into the corresponding number of groups of AC energy-consuming devices. The second preset formula is: Among them, N 交流耗能装置组数 is the number of groups of AC energy-consuming devices to be invested, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices; S10. After each sending - end flexible DC converter station and receiving - end flexible DC converter station detect that the DC voltage has recovered to the preset value, the sending - end flexible DC converter station cuts off the AC energy - consuming devices in groups, restores the DC current, and completes the restart of the DC fault.

2. The DC fault self-clearing method for the new energy island power grid transmission system according to claim 1, characterized in that Before step S10, it also includes: S010. When the de - ionization time is reached, each sending - end flexible DC converter station and receiving - end flexible DC converter station restore the slope of the DC reference value input to the DC power controller of the faulty pole. Each sending - end flexible DC converter station and receiving - end flexible DC converter station cut back the active current command of the faulty pole to be controlled by the outer - loop controller, and restore the DC voltage.

3. The DC fault self-clearing method for the new energy island power grid transmission system according to claim 2, wherein The de - ionization time is 300 ms to 400 ms.

4. The DC fault self-clearing method for the new energy island power grid transmission system according to claim 1, characterized in that, The new - energy power field includes a wind farm and a photovoltaic power field.

5. The DC fault self-clearing method for the new energy island power grid transmission system according to claim 1, characterized in that, The number of sending - end flexible DC converter stations is one or more than two, and the number of receiving - end flexible DC converter stations is one or more than two.

6. A new energy island power grid transmission system, characterized in that, It includes a new - energy power field, a sending - end flexible DC converter station, a receiving - end flexible DC converter station, a DC overhead line, and an AC energy - consuming device. The new - energy power field is commonly connected to the sending - end flexible DC converter station through a three - phase AC bus. The AC energy - consuming device is connected between the new - energy power field and the sending - end flexible DC converter station. The sending - end flexible DC converter station is connected to the receiving - end flexible DC converter station through a bipolar DC overhead line. The sending - end flexible DC converter station, the DC overhead line, and the receiving - end flexible DC converter station form a true bipolar DC system; All sending - end flexible DC converter stations adopt a double - closed - loop control strategy of constant AC voltage and frequency. Only one receiving - end flexible DC converter station adopts a constant DC voltage control strategy, and the remaining receiving - end flexible DC converter stations adopt a constant active power control strategy; When the new - energy island power grid sending system is in operation, each sending - end flexible DC converter station and receiving - end flexible DC converter station detect the DC voltage and current in real time, and judge whether a DC fault occurs in the line according to the DC voltage and current. If so, steps A1 and B1 are executed simultaneously; When the new - energy island power grid sending system is in operation, each pole of the sending - end flexible DC converter station detects the DC current flowing out of this pole in real time. If it detects that the DC current flowing out of this pole increases, this pole automatically reduces the DC voltage offset through the DC controller, reduces the number of arm sub - modules put into the DC side, directly controls the DC voltage, and outputs a negative DC voltage to actively eliminate the DC fault; When the new - energy island power grid sending system is in operation, each pole of the receiving - end flexible DC converter station detects the DC current flowing into this pole in real time. If it detects that the DC current flowing into this pole decreases and reversely increases, this pole automatically reduces the DC voltage offset through the DC current controller, reduces the number of arm sub - modules put into the DC side, directly controls the DC voltage, and outputs a negative DC voltage to actively eliminate the DC fault; A1. After detecting a DC fault, the control systems of each sending-end and receiving-end flexible DC converter station enter the deionization logic. Each sending-end and receiving-end flexible DC converter station sets the DC current reference value input to the DC current controller of the faulty pole to zero for zero DC current control. At the same time, each sending-end and receiving-end flexible DC converter station sets the active current command input to the outer-loop controller of the faulty pole to zero. B1. After detecting a DC fault, determine whether the true bipolar DC system is operating in bipolar mode. If so, execute step B2; if not, execute step B3. B2. Transfer the power of the faulty pole to the non-faulty pole. If there is still power surplus at the sending end, calculate the number of groups of AC energy-consuming devices to be put into operation according to the first preset formula, and put into operation the corresponding number of groups of AC energy-consuming devices. The first preset formula is: P 送端正常极剩余容量 = P 额定功率 - P 送端正常极 Among them, P 送端正常极剩余容量 is the remaining capacity of the normal pole of the sending-end flexible DC converter station, P 额定功率 is the rated power of the sending-end flexible DC converter station, P 送端正常极 is the active power of the normal pole of the sending-end flexible DC converter station, N 交流耗能装置组数 is the number of AC energy-consuming device groups to be put into operation, P 送端双极功率 is the active power of the bipolar operation of the sending-end flexible DC converter station, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices; B3. Calculate the number of groups of AC energy-consuming devices to be put into operation according to the second preset formula, and put into operation the corresponding number of groups of AC energy-consuming devices. The second preset formula is: Among them, N 交流耗能装置组数 is the number of AC energy-consuming device groups to be invested, P 送端故障极 is the active power of the faulty pole of the sending-end flexible DC converter station, P 每组交流耗能装置容量 is the capacity of each group of AC energy-consuming devices; When each sending-end and receiving-end flexible DC converter station in the new energy island power grid sending system detects that the DC voltage has recovered to the preset value, the sending-end flexible DC converter station removes the AC energy-consuming devices in groups, restores the DC current, and completes the restart of the DC fault.

7. The new energy island power grid transmission system according to claim 6, characterized in that, Before each sending-end and receiving-end flexible DC converter station in the new energy island power grid sending system detects that the DC voltage has recovered to the preset value, the sending-end flexible DC converter station removes the AC energy-consuming devices in groups, restores the DC current, and completes the restart of the DC fault, the new energy island power grid sending system also performs the following operations: When the deionization time is reached, each sending-end and receiving-end flexible DC converter station restores the slope of the DC reference value input to the DC power controller of the faulty pole, and each sending-end and receiving-end flexible DC converter station switches the active current command of the faulty pole back to be controlled by the outer-loop controller to restore the DC voltage.

8. The new energy island power grid transmission system according to claim 7, characterized in that, The deionization time is 300 ms to 400 ms.

9. The new energy island power grid transmission system according to claim 6, characterized in that, The new energy power field includes a wind farm and a photovoltaic power field.

10. The new energy island power grid transmission system according to claim 6, characterized in that, The number of sending-end flexible DC converter stations is one or more than two, and the number of receiving-end flexible DC converter stations is one or more than two.

Images