Fault ride-through method and system for a new energy hybrid DC transmission system

Abstract

The present invention relates to a fault ride-through method and system for a new energy hybrid DC transmission system, including: when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, recording the duration of the fault and obtaining the actual voltage of the DC line in the new energy hybrid DC transmission system; adjusting the unloading circuit and circuit breaker provided in the new energy hybrid DC transmission system according to the fault duration of the new energy hybrid DC transmission system and the actual voltage of the DC line, so that the new energy hybrid DC transmission system can achieve fault ride-through. The present invention enables the new energy hybrid DC transmission system to still operate stably after a fault occurs, without excessive restriction on the power generation of new energy, reduces power waste, and improves the efficiency of the system's transmission power.

Description

Technical Field

[0001] The present invention relates to the field of simulation technology in hybrid DC interconnection technology, and particularly relates to a fault ride-through method and system for a new energy hybrid DC transmission system. Background Art

[0002] On the new energy side such as photovoltaic and wind energy, voltage source converter (VSC) technology is used for step-up and aggregation. After aggregation, it is sent out through a high-voltage DC transmission line by using the power electronic interface of a voltage source converter station through a hybrid DC interconnection interface. At the receiving end, an LCC converter station is used to invert the new energy into the AC power grid, which has become an important trend in the application of new energy in China. In order to realize the start-up and transmission of new energy, the hybrid DC interconnection interface needs to realize the forward and reverse transmission of power. An isolated topology structure with two sets of modular multilevel converters connected through the AC side can realize the inversion of hybrid DC, which is one of the options for the hybrid DC interconnection interface. New energy generation is all current sources, and its AC voltage support is provided by the sending-end VSC. When an AC fault occurs at the receiving end, the DC line voltage will drop to varying degrees, but the DC line can still operate under low current conditions, and the power transmitted by the DC network will also drop severely. If the new energy side does not limit the power output, the accumulated electrical energy will converge on the capacitors in the link, resulting in device damage. In order to ensure the stable power transmission of the system, it is necessary to study the fault response characteristics of the new energy transmission system when an AC fault occurs in the receiving-end AC system, and analyze the method of fault ride-through of the hybrid DC interconnection interface, so as to ensure the continuous and stable operation of the new energy transmission system under receiving-end faults. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a fault ride-through method and system for a new energy hybrid DC transmission system. When an AC fault occurs in the receiving-end AC power grid of the new energy hybrid DC transmission system, the system can maintain normal operation for a short time; when the DC voltage is restored to a certain extent, the system can transmit electrical energy to the receiving end to assist the receiving-end AC power grid to resume normal operation.

[0004] The purpose of the present invention is achieved by the following technical solutions:

[0005] The present invention provides a fault ride-through method for a new energy hybrid DC transmission system, which is improved in that the method includes:

[0006] When an AC fault occurs in the receiving-end AC power grid of the new energy hybrid DC transmission system, record the duration of the fault and obtain the actual voltage of the DC line in the new energy hybrid DC transmission system;

[0007] Set the unloading circuit and circuit breaker in the new energy hybrid DC transmission system according to the fault duration of the new energy hybrid DC transmission system and the actual voltage regulation of the DC line, so that the new energy hybrid DC transmission system can achieve fault ride-through;

[0008] Among them, the circuit breaker is set between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the receiving-end LCC converter station, and the unloading circuits are respectively set between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker and between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the voltage source converter in the new energy hybrid DC transmission system.

[0009] Preferably, the setting of the unloading circuit and circuit breaker in the new energy hybrid DC transmission system according to the fault duration of the new energy hybrid DC transmission system and the actual voltage regulation of the DC line, so that the new energy hybrid DC transmission system can achieve fault ride-through, includes:

[0010] Step 1: Starting from the moment when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, set three preset time points t1, t2, and t3 in sequence, and set the threshold voltage of the DC line;

[0011] Step 2: Judge whether the actual voltage of the DC line is less than the threshold voltage;

[0012] If the actual voltage of the DC line is less than the threshold voltage, execute Step 3;

[0013] If the actual voltage of the DC line is greater than the threshold voltage, execute Step 4;

[0014] Step 3: The unloading circuits set between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker and between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the voltage source converter are all put into use;

[0015] If the fault is eliminated before the moment of t1, the unloading circuits set between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker and between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the voltage source converter stop working; otherwise, when the fault duration reaches the moment of t1, the circuit breaker disconnects;

[0016] If the fault is eliminated before the moment of t2, the circuit breaker closes, the unloading circuits set between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker and between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the voltage source converter stop working, and the hybrid DC interconnection interface switches to the constant power or constant current control mode; otherwise, when the fault duration reaches the moment of t2, the new energy hybrid DC transmission system stops working;

[0017] Step 4: The unloading circuit provided between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker is put into use;

[0018] If the fault is eliminated before time t3, the unloading circuit between the hybrid DC interconnection interface and the receiving-end AC grid in the new energy hybrid DC transmission system stops working;

[0019] Otherwise, when the fault duration reaches time t3, the new energy hybrid DC transmission system adjusts the power generation of the new energy according to the maximum power it can transmit, or shuts down the new energy according to the dispatching instruction, and restarts power generation after the fault at the receiving end is eliminated.

[0020] Preferably, the threshold voltage is half of the rated voltage of the DC line.

[0021] Preferably, the initial state of the circuit breaker is closed.

[0022] Preferably, the hybrid DC interconnection interface is composed of a first modular multilevel converter and a second modular multilevel converter connected to each other through the AC side.

[0023] An improved fault ride-through system for a new energy hybrid DC transmission system, wherein the system comprises:

[0024] A recording module, configured to record the duration of a fault and obtain the actual voltage of the DC line in the new energy hybrid DC transmission system when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system;

[0025] An adjustment module, configured to adjust the unloading circuit and the circuit breaker provided in the new energy hybrid DC transmission system according to the fault duration of the new energy hybrid DC transmission system and the actual voltage of the DC line, so that the new energy hybrid DC transmission system can achieve fault ride-through;

[0026] Wherein, the circuit breaker is provided between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the receiving-end LCC converter station, and the unloading circuits are respectively provided between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker and between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the voltage source converter in the new energy hybrid DC transmission system.

[0027] Preferably, the adjustment module is configured to:

[0028] Step 1: Starting from the moment when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, three preset time points t1, t2 and t3 are set in sequence, and the threshold voltage of the DC line is set;

[0029] Step 2: Determine whether the actual voltage of the DC line is less than the threshold voltage;

[0030] If the actual voltage of the DC line is less than the threshold voltage, execute Step 3;

[0031] If the actual voltage of the DC line is greater than the threshold voltage, execute Step 4;

[0032] Step 3: The unloading circuits between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker, and between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the voltage source converter are all put into use;

[0033] If the fault is eliminated before time t1, the unloading circuits between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker, and between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the voltage source converter stop working; otherwise, when the fault duration reaches time t1, the circuit breaker disconnects;

[0034] If the fault is eliminated before time t2, the circuit breaker closes, the unloading circuits between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker, and between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the voltage source converter stop working, and the hybrid DC interconnection interface switches to the constant power or constant current control mode; otherwise, when the fault duration reaches time t2, the new energy hybrid DC transmission system stops working;

[0035] Step 4: The unloading circuit between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker is put into use;

[0036] If the fault is eliminated before time t3, the unloading circuit between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the receiving-end AC grid stops working;

[0037] Otherwise, when the fault duration reaches time t3, the new energy hybrid DC transmission system adjusts the power generation of the new energy according to the maximum power it can transmit, or shuts down the new energy according to the dispatching instruction, and restarts power generation after the receiving-end fault is eliminated.

[0038] Further, the threshold voltage is half of the rated voltage of the DC line.

[0039] Preferably, the initial state of the circuit breaker is closed.

[0040] Preferably, the hybrid DC interconnection interface is composed of a first modular multilevel converter and a second modular multilevel converter connected to each other through the AC side.

[0041] Compared with the closest prior art, the beneficial effects of the present invention are as follows:

[0042] According to the technical solution provided by the present invention, when a fault occurs in the receiving-end AC power grid of the new energy hybrid DC transmission system, the duration of the fault is recorded and the actual voltage of the DC line in the new energy hybrid DC transmission system is obtained; the unloading circuit and circuit breaker provided in the new energy hybrid DC transmission system are adjusted according to the fault duration of the new energy hybrid DC transmission system and the actual voltage of the DC line, so that the new energy hybrid DC transmission system can still operate stably after the fault occurs, without excessive restriction on the power generation of new energy, reducing power waste and improving the efficiency of system transmission power. Brief Description of the Drawings

[0043] Figure 1 is a flowchart of a fault ride-through method for a new energy hybrid DC transmission system provided by the present invention;

[0044] Figure 2 is a structure diagram of a new energy hybrid DC transmission system provided by an embodiment of the present invention;

[0045] Figure 3 is a flowchart of a fault ride-through method for a new energy hybrid DC transmission system provided by an embodiment of the present invention;

[0046] Figure 4 is a structure diagram of a hybrid DC interconnection interface in a new energy hybrid DC transmission system provided by an embodiment of the present invention;

[0047] Figure 5 is a schematic structural diagram of a fault ride-through system for a new energy hybrid DC transmission system provided by the present invention. Detailed Description of the Embodiments

[0048] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings.

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. 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.

[0050] After a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, the voltage on the side of the hybrid DC interconnection interface close to the LCC converter station will drop, and the voltage on the side of the hybrid DC interconnection interface close to the VSC will also fluctuate at one end. The power transmission capacity of the LCC converter station decreases, resulting in power imbalance in the new energy hybrid DC transmission system, leading to energy accumulation and damage to instruments. The solution provided by the present invention is as follows.

[0051] The present invention provides a fault ride-through method for a new energy hybrid DC transmission system, as Figure 1 shown, including:

[0052] Step 101: When a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, record the duration of the fault and obtain the actual voltage of the DC line in the new energy hybrid DC transmission system;

[0053] Step 102: Adjust the unloading circuit and circuit breaker set in the new energy hybrid DC transmission system according to the fault duration of the new energy hybrid DC transmission system and the actual voltage of the DC line, so that the new energy hybrid DC transmission system can achieve fault ride-through;

[0054] As Figure 2 shown, wherein, the circuit breaker is set between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the receiving-end LCC converter station, and the unloading circuit is respectively set between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker, and between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the voltage source converter in the energy hybrid DC transmission system.

[0055] Specifically, the step 102, as Figure 3 shown, includes:

[0056] Step 1: Starting from the moment when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, sequentially set three preset time points t1, t2, and t3, and set the threshold voltage u1 of the DC line;

[0057] Step 2: Determine whether the actual voltage of the DC line is less than the threshold voltage;

[0058] If the actual voltage of the DC line is less than the threshold voltage u1, execute step 3;

[0059] If the actual voltage of the DC line is greater than the threshold voltage u1, execute step 4;

[0060] Step 3: The unloading circuits provided between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker, and between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the voltage source converter are put into use. The hybrid DC interconnection interface switches to the voltage control mode, and the two-side unloading circuits consume the power generated by the new energy simultaneously;

[0061] If the fault is eliminated before time t1, the converter recovers its voltage control ability, the hybrid DC interconnection interface resumes the power transmission mode, the unloading circuits provided between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker, and between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the voltage source converter stop working, and the DC line resumes the normal transmission of new energy, and the fault ride-through process ends; Otherwise, when the fault duration reaches time t1, the circuit breaker trips;

[0062] If the fault is eliminated before time t2, the circuit breaker closes, the unloading circuits provided between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker, and between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the voltage source converter stop working, the hybrid DC interconnection interface switches to the constant power or constant current control mode, and the whole system resumes normal operation, and the fault ride-through process ends; Otherwise, when the fault duration reaches time t2, the new energy hybrid DC transmission system stops working;

[0063] Step 4: The unloading circuit provided between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker is put into use. The power that can be output and the current that can be borne are calculated according to the proportion of the DC voltage drop, and dynamic switching is performed to consume the excess power;

[0064] If the fault is eliminated before time t3, the unloading circuit between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the receiving-end AC grid stops working, and the line resumes the normal transmission of new energy, and the fault ride-through process ends;

[0065] Otherwise, when the fault duration reaches time t3, the new energy hybrid DC transmission system adjusts the power generation of the new energy according to the maximum power that can be sent, or shuts down the new energy according to the dispatching instruction, and restarts the power generation after the fault at the receiving end is eliminated.

[0066] The threshold voltage is half of the rated voltage of the DC line.

[0067] The initial state of the circuit breaker is closed.

[0068] As Figure 4 shown, the hybrid DC interconnection interface is composed of a first modular multilevel converter and a second modular multilevel converter connected to each other through the AC side.

[0069] The present invention also provides a fault ride-through system for a new energy hybrid DC transmission system, as Figure 5 shown, the system includes:

[0070] A recording module, configured to record the duration of a fault and obtain the actual voltage of the DC line in the new energy hybrid DC transmission system when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system;

[0071] An adjustment module, configured to adjust the unloading circuit and the circuit breaker provided in the new energy hybrid DC transmission system according to the fault duration of the new energy hybrid DC transmission system and the actual voltage of the DC line, so that the new energy hybrid DC transmission system can achieve fault ride-through;

[0072] Wherein, the circuit breaker is arranged between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the receiving-end LCC converter station, and the unloading circuits are respectively arranged between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker and between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the voltage source converter in the new energy hybrid DC transmission system.

[0073] The adjustment module is configured to:

[0074] Step 1: Starting from the moment when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, sequentially set three preset time points t1, t2, and t3, and set the threshold voltage u1 of the DC line;

[0075] Step 2: Determine whether the actual voltage of the DC line is less than the threshold voltage;

[0076] If the actual voltage of the DC line is less than the threshold voltage u1, execute Step 3;

[0077] If the actual voltage of the DC line is greater than the threshold voltage u1, execute Step 4;

[0078] Step 3: The unloading circuits arranged between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the circuit breaker and between the hybrid DC interconnection interface of the new energy hybrid DC transmission system and the voltage source converter are both put into use, the hybrid DC interconnection interface switches to the voltage control mode, and the two-side unloading circuits consume the power generated by the new energy simultaneously;

[0079] If the fault is cleared before time t1, the converter recovers its voltage control ability, the hybrid DC interconnection interface resumes the power transmission mode, the unloading circuits provided between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the circuit breaker, and between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the voltage source converter stop working, the DC line resumes normal new energy transmission, and the fault ride-through process ends; otherwise, when the fault duration reaches time t1, the circuit breaker trips.

[0080] If the fault is cleared before time t2, the circuit breaker closes, the unloading circuits provided between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the circuit breaker, and between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the voltage source converter stop working, the hybrid DC interconnection interface switches to the constant power or constant current control mode, and the whole system resumes normal operation, and the fault ride-through process ends; otherwise, when the fault duration reaches time t2, the new energy hybrid DC transmission system stops working.

[0081] Step 4: The unloading circuit provided between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the circuit breaker is put into use, calculates the power that can be output and the current that can be borne according to the proportion of the DC voltage drop, and performs dynamic switching to consume the excess power.

[0082] If the fault is cleared before time t3, the unloading circuit between the hybrid DC interconnection interface in the new energy hybrid DC transmission system and the receiving-end AC grid stops working, and the line resumes normal new energy transmission, and the fault ride-through process ends.

[0083] Otherwise, when the fault duration reaches time t3, the new energy hybrid DC transmission system adjusts the power output of the new energy according to the maximum power that can be sent out, or shuts down the new energy according to the dispatching instruction, and restarts power generation after the fault at the receiving end is cleared.

[0084] The threshold voltage is half of the rated voltage of the DC line.

[0085] The initial state of the circuit breaker is closed.

[0086] The hybrid DC interconnection interface is composed of a first modular multilevel converter and a second modular multilevel converter connected to each other through the AC side.

[0087] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0088] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one or more of the processes Figure 1 or blocks.

[0089] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in Figure 1 one or more of the processes Figure 1 or blocks.

[0090] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are performed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one or more of the processes Figure 1 or blocks.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A fault ride-through method for a new energy hybrid DC transmission system, characterized in that, The method includes: When a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, record the duration of the fault and obtain the actual voltage of the DC line in the new energy hybrid DC transmission system; Adjust the unloading circuit and circuit breaker set in the new energy hybrid DC transmission system according to the fault duration of the new energy hybrid DC transmission system and the actual voltage of the DC line, so that the new energy hybrid DC transmission system can achieve fault ride-through, including: Step 1: Starting from the moment when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, set in sequence , and three preset time points, and set the threshold voltage of the DC line; Step 2: Determine whether the actual voltage of the DC line is less than the threshold voltage; If the actual voltage of the DC line is less than the threshold voltage, execute Step 3; If the actual voltage of the DC line is greater than the threshold voltage, execute Step 4; Step 3: The unloading circuits between the hybrid DC interconnection interface and the circuit breaker in the new energy hybrid DC transmission system and between the hybrid DC interconnection interface and the voltage source converter are both put into use; If the fault is eliminated before time, the unloading circuits provided between the hybrid DC interconnection interface and the circuit breaker and between the hybrid DC interconnection interface and the voltage source converter stop working; otherwise, when the fault duration reaches time, the circuit breaker trips; If the fault is eliminated before time, the circuit breaker closes, the unloading circuits provided between the hybrid DC interconnection interface and the circuit breaker and between the hybrid DC interconnection interface and the voltage source converter stop working, and the hybrid DC interconnection interface switches to the constant power or constant current control mode; otherwise, when the fault duration reaches time, the new energy hybrid DC transmission system stops working; Step 4: The unloading circuit between the hybrid DC interconnection interface and the circuit breaker is put into use; If the fault is eliminated before the unloading circuit between the hybrid DC interconnection interface and the receiving AC grid stops working; Otherwise, when the fault duration reaches the moment, the new energy hybrid DC transmission system adjusts the output power of new energy according to the maximum power it can transmit, or shuts down the new energy according to the dispatching instruction, and restarts power generation after the fault at the receiving end is eliminated; Wherein, the circuit breaker is set between the hybrid DC interconnection interface and the receiving-end LCC converter station, and the unloading circuits are respectively set between the hybrid DC interconnection interface and the circuit breaker and between the hybrid DC interconnection interface and the voltage source converter.

2. The method according to claim 1, characterized in that, The threshold voltage is half of the rated voltage of the DC line.

3. The method according to claim 1, characterized in that, The initial state of the circuit breaker is closed.

4. The method according to claim 1, characterized in that, The hybrid DC interconnection interface is composed of a first modular multilevel converter and a second modular multilevel converter connected to each other through the AC side.

5. A fault ride-through system for a new energy hybrid DC transmission system, characterized in that, The system includes: A recording module, which is used to record the duration of the fault and obtain the actual voltage of the DC line in the new energy hybrid DC transmission system when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system; An adjustment module, which is used to adjust the unloading circuit and circuit breaker set in the new energy hybrid DC transmission system according to the fault duration of the new energy hybrid DC transmission system and the actual voltage of the DC line, so that the new energy hybrid DC transmission system can achieve fault ride-through; Wherein, the circuit breaker is set between the hybrid DC interconnection interface and the receiving-end LCC converter station of the new energy hybrid DC transmission system, and the unloading circuits are respectively set between the hybrid DC interconnection interface and the circuit breaker and between the hybrid DC interconnection interface and the voltage source converter in the new energy hybrid DC transmission system; The adjustment module is used for: Step 1: Starting from the moment when a fault occurs in the receiving-end AC grid of the new energy hybrid DC transmission system, set successively , and three preset time points, and set the threshold voltage of the DC line; Step 2: Determine whether the actual voltage of the DC line is less than the threshold voltage; If the actual voltage of the DC line is less than the threshold voltage, execute Step 3; If the actual voltage of the DC line is greater than the threshold voltage, execute Step 4; Step 3: The unloading circuits between the hybrid DC interconnection interface and the circuit breaker and between the hybrid DC interconnection interface and the voltage source converter are both put into use; If the fault is eliminated before the time, the unloading circuits provided between the hybrid DC interconnection interface and the circuit breaker and between the hybrid DC interconnection interface and the voltage source converter stop working; otherwise, when the fault duration reaches the time, the circuit breaker trips; If the fault is eliminated before the moment, the circuit breaker closes, the unloading circuits arranged between the hybrid DC interconnection interface and the circuit breaker and between the hybrid DC interconnection interface and the voltage source converter stop working, and the hybrid DC interconnection interface switches to the constant power or constant current control mode; otherwise, when the fault duration reaches the moment, the new energy hybrid DC transmission system stops working; Step 4: The unloading circuit between the hybrid DC interconnection interface and the circuit breaker is put into use; If the fault is eliminated before the unloading circuit between the hybrid DC interconnection interface and the receiving-end AC grid stops working; Otherwise, when the fault duration reaches the time, the new energy hybrid DC transmission system adjusts the output power of new energy according to the maximum power that can be transmitted, or shuts down the new energy according to the dispatching instruction, and restarts power generation after the fault at the receiving end is eliminated.

6. The system according to claim 5, characterized in that, The threshold voltage is half of the rated voltage of the DC line.

7. The system according to claim 5, characterized in that, The initial state of the circuit breaker is closed.

8. The system according to claim 5, characterized in that, The hybrid DC interconnection interface is composed of a first modular multilevel converter and a second modular multilevel converter connected to each other through the AC side.

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