Improved bridge type fault current limiter and direct current transmission control method and system

Abstract

The invention relates to an improved bridge type fault current limiter and a direct current transmission control method and system. The fault current limiter comprises a bridge type current limiting circuit and a shunt branch arranged on a bridge arm of the bridge type current limiting circuit. The shunt branch comprises a first shunt circuit, a second shunt circuit and an IGBT. The first shunt circuit comprises a first resistor and a first inductor which are connected in series; the second shunt circuit comprises a second resistor and a second inductor which are connected in series; an emitter and a collector of the IGBT are connected in parallel with the second shunt circuit, and a grid of the IGBT is connected with the control unit; and a parallel circuit of the second shunt circuit and the IGBT is connected in series with the first shunt circuit.

Description

Technical Field

[0001] The invention relates to an improved bridge fault current limiter, a direct current transmission control method and a system, and belongs to the technical field of power control. Background Art

[0002] Due to the many advantages of modular multilevel converters (MMC) in high-voltage and large-capacity power conversion situations, DC grids based on MMC have gradually become the development trend of future DC transmission projects. However, DC grids have the characteristics of "low inertia and low impedance". After a short-circuit fault occurs on the DC side, the DC current changes rapidly. Studies have shown that quickly cutting off the fault line based on high-voltage DC circuit breakers is one of the protection schemes currently suitable for handling DC faults in DC grids. In order to reduce the rising rate of fault current, reduce the current stress of the DC circuit breaker during breaking, and reduce the cost of the DC circuit breaker, DC current limiters have emerged. Smoothing reactors are often added at both ends of the DC line and current limiting reactors are added to the DC circuit breaker. However, the increase in the reactor not only increases the construction cost, but also affects the dynamic characteristics of the entire DC system, causing some modes of the entire DC system to show weak damping, thereby causing system instability. In order to solve the above problems, it is of great significance to study DC fault current limiters suitable for DC systems.

[0003] At present, there are many studies on the topology and control strategy structure of DC current limiters. D. Keshavarzi proposed a new type of DC fault current limiter (ADFCC) designed for grid-connected photovoltaic systems to solve the problem of uncontrolled fault current caused by the widespread integration of such systems. ADFCC uses a complex control algorithm to manage its internal semiconductor switches to effectively limit the fault current. The system can effectively limit the fault current under both balanced and unbalanced fault conditions, enhancing the dynamic performance and stability of the power grid. However, the design and implementation of ADFCC are relatively complex and may involve higher costs, and its performance depends largely on the accuracy of the control system design. In another study, Li Chunhua designed an inductive current limiter to solve the problem of commutation failure caused by increased DC current. The current limiter is based on the characteristics of inductance passing low frequencies and blocking high frequencies, and uses fast and controllable power electronic devices to realize the conversion of DC current to AC current. It can be installed at the DC outlet of the inverter station of the high-voltage DC transmission system. However, the inductive current limiter requires high-performance power electronic devices, which may lead to high costs; the design and control strategy are relatively complex, requiring precise parameter adjustment and control algorithms. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention proposes an improved bridge fault current limiter, a direct current transmission control method and a system.

[0005] The technical solution of the present invention is as follows:

[0006] In one aspect, the present invention provides an improved bridge fault current limiter, comprising:

[0007] A bridge current limiting circuit and a shunt branch arranged on a bridge arm of the bridge current limiting circuit;

[0008] The shunt branch includes a first shunt circuit, a second shunt circuit and an IGBT;

[0009] The first shunt circuit includes a first resistor and a first inductor connected in series, and the second shunt circuit includes a second resistor and a second inductor connected in series;

[0010] The emitter and collector of the IGBT are connected in parallel with the second shunt circuit, and the gate of the IGBT is connected to the control unit;

[0011] The parallel circuit of the second shunt circuit and the IGBT is connected in series with the first shunt circuit.

[0012] On the other hand, the present invention also proposes a DC power transmission control method based on an improved bridge fault current limiter, comprising the following steps:

[0013] An improved bridge fault current limiter and a nonlinear controller as described in any embodiment of the present invention are arranged in each phase between a DC power source and a power grid, and the generator transmits power to the power grid through the improved bridge fault current limiter;

[0014] The nonlinear controller monitors the instantaneous phase voltage at the common coupling point of the power grid in real time and detects power grid faults according to the instantaneous phase voltage;

[0015] When no grid fault is detected, the nonlinear controller sends a control signal with a signal value of 1 to the gate of the IGBT;

[0016] When a grid fault is detected, the nonlinear controller nonlinearly calculates the deviation between the instantaneous phase voltage and the reference voltage, outputs a nonlinear calculation value, generates a duty cycle according to the nonlinear calculation value, and outputs a PWM control signal to the gate of the IGBT through the PWM generator based on the duty cycle.

[0017] As a preferred implementation, the step of detecting a power grid fault according to the instantaneous phase voltage is specifically as follows:

[0018] Get the instantaneous phase voltage as V d,φ , for V d,φ A quarter-cycle delay produces a corresponding voltage V q,φ , calculate the comparison voltage according to the following formula:

[0019]

[0020] Among them, V dq,φ is the comparison voltage;

[0021] V dq,φ With the preset voltage threshold V th Compare and determine whether the power grid has failed.

[0022] As a preferred implementation, in the step of nonlinearly calculating the deviation between the instantaneous phase voltage and the reference voltage by the nonlinear controller, the nonlinear function used is:

[0023] d=1-e -kΔV ;

[0024] Where d is the nonlinear calculation value, k is the adjustment coefficient, and ΔV is the deviation between the instantaneous phase voltage and the reference voltage.

[0025] On the other hand, the present invention further provides a DC power transmission control system based on an improved bridge fault current limiter, comprising:

[0026] A DC power source, an improved bridge fault current limiter as described in any embodiment of the present invention, and a nonlinear controller;

[0027] Each phase between the DC power source and the power grid is provided with an improved bridge fault current limiter and a nonlinear controller, and the generator transmits power to the power grid through the improved bridge fault current limiter;

[0028] The nonlinear controller monitors the instantaneous phase voltage at the common coupling point of the power grid in real time and detects power grid faults according to the instantaneous phase voltage;

[0029] When no grid fault is detected, the nonlinear controller sends a control signal with a signal value of 1 to the gate of the IGBT;

[0030] When a grid fault is detected, the nonlinear controller nonlinearly calculates the deviation between the instantaneous phase voltage and the reference voltage, outputs a nonlinear calculation value, generates a duty cycle according to the nonlinear calculation value, and outputs a PWM control signal to the gate of the IGBT through the PWM generator based on the duty cycle.

[0031] As a preferred implementation, the steps of the nonlinear controller detecting a power grid fault according to the instantaneous phase voltage are specifically as follows:

[0032] Get the instantaneous phase voltage as V d,φ , for V d,φ A quarter-cycle delay produces a corresponding voltage V q,φ , calculate the comparison voltage according to the following formula:

[0033]

[0034] Among them, Vdq,φ is the comparison voltage;

[0035] V dq,φ With the preset voltage threshold V th Compare and determine whether the power grid has failed.

[0036] As a preferred implementation, in the step of nonlinearly calculating the deviation between the instantaneous phase voltage and the reference voltage by the nonlinear controller, the nonlinear function used is:

[0037] d=1-e -kΔV ;

[0038] Where d is the nonlinear calculation value, k is the adjustment coefficient, and ΔV is the deviation between the instantaneous phase voltage and the reference voltage.

[0039] On the other hand, the present invention further proposes an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the direct current transmission control method based on the improved bridge fault current limiter as described in any embodiment of the present invention is implemented.

[0040] On the other hand, the present invention further provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the DC power transmission control method based on the improved bridge fault current limiter as described in any embodiment of the present invention.

[0041] Additional aspects and advantages of the present invention will be set forth in the following description, and some of them will be apparent from the description, or may be understood by practicing the present invention. In addition, the various aspects and advantages of the present invention may be realized and obtained by the method steps and combinations particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of a fault current limiter circuit according to Embodiment 1 of the present invention;

[0043] Figure 2 Schematic diagram of control logic of a nonlinear controller in Embodiment 2 of the present invention;

[0044] Figure 3 This is an example diagram of a voltage deviation index experiment corresponding to different adjustment coefficients k in an embodiment of the present invention;

[0045] Figure 4 A schematic diagram of a system simulation model of Embodiment 3 of the present invention;

[0046] Figure 5 It is a control block diagram of an external controller of a distributed DC power supply controller in an embodiment of the present invention;

[0047] Figure 6 This is a control block diagram of an internal controller of a distributed DC power supply controller in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] It should be understood that the step numbers used in this document are only for convenience of description and are not intended to limit the order in which the steps are executed.

[0050] It should be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0051] The terms “include” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0052] The term "and / or" means and includes any and all possible combinations of one or more of the associated listed items.

[0053] Embodiment 1:

[0054] DC current limiter technology plays an important role in controlling and limiting fault currents in power systems. First, cost is a major issue, especially for superconducting current limiters, which require the use of special superconducting materials and complex cooling systems, which makes their manufacturing and maintenance costs relatively high. These costs limit the application of superconducting current limiters in a wider range of situations. Secondly, technical challenges and complexity are also factors that limit the application of DC current limiters. The operation of superconducting current limiters depends on the superconducting material to maintain the superconducting state, which involves precise temperature and magnetic field control. Once a fault occurs, the superconducting material may lose its superconductivity and complex technology is required to restore its performance. Third, performance limitations are also a problem. The response speed and current limiting effect of superconducting current limiters are limited by their material properties, and it takes a long time to recover to the superconducting state after a fault, which affects their application in situations that require a fast response. Finally, the complexity of actual deployment and maintenance is also one of the disadvantages of DC current limiters. Superconducting current limiters require professional technical support for installation and commissioning, and have high maintenance requirements for cooling systems and superconducting materials, all of which increase the difficulty and cost of application.

[0055] Although superconducting fault current limiters are very effective in improving low voltage ride-through and fault ride-through capabilities, limiting fault currents and enhancing transient stability of power systems, and are superior in reliability, fault current limiting and low steady-state losses, non-superconducting fault current limiters have also attracted the attention of researchers due to their low cost, fast switching speed, no recovery time and potential scope for improvement. Bridge fault current limiters are one of the most widely used non-superconducting fault current limiters in various wind farms, smart grids, distribution networks, etc.

[0056] In summary, in order to improve the stability of the DC power transmission system and the ability to cope with grid faults, this embodiment proposes an improved bridge fault current limiter (MBFCL) to keep the fault current within a controllable range, thereby ensuring system safety when a short circuit fault occurs.

[0057] See Figure 1 The improved bridge fault current limiter (MBFCL) provided in this embodiment is an improved version of the bridge fault DC current limiter (BFCL). The improved bridge fault current limiter is different from the traditional typical BFCL and does not have any isolated shunt branches and bridge branches. In the improved bridge fault current limiter, the shunt branch is placed on the bridge arm and connected in parallel with the insulated gate bipolar transistor (IGBT).

[0058] The improved bridge fault current limiter specifically comprises:

[0059] A bridge current limiting circuit composed of diodes D1, D2, D3, and D4, and a shunt branch arranged on a bridge arm of the bridge current limiting circuit;

[0060] The shunt branch includes a first shunt circuit, a second shunt circuit and an IGBT;

[0061] The first shunt circuit includes a first resistor R in series DC and the first inductor L DC The second shunt circuit includes a second resistor D in series SH and the second inductor L SH ;

[0062] The emitter and collector of the IGBT are connected in parallel with the second shunt circuit, and the gate of the IGBT is connected to the control unit;

[0063] The parallel circuit of the second shunt circuit and the IGBT is connected in series with the first shunt circuit.

[0064] The improved bridge fault current limiter of this embodiment has two operating states: a steady state and a fault state.

[0065] Current flows through D1 / D2-L in steady state DC -R DC -IGBT-D4 / D3, current flows through D1 / D2-L in fault state DC -R DC -R SH DC generator L SH -D4 / D3. The switching between steady state and fault state is controlled by the control unit of MBFCL. DC It is a small inductor that can suppress the rapid increase of fault current at the beginning of a fault to protect the IGBT switch from the huge di / dt. SH Its function is to limit the growth of fault current when a fault occurs, thereby protecting the system from damage caused by excessive current. SH With R SH Working together, under fault conditions, they limit the fault current by increasing the impedance of the circuit. The inductor is able to limit the rate of change of current (di / dt), which is critical to protecting the IGBT switch and other system components from damage caused by a sudden rise in fault current. SH and L SH The combined use of the two enables the MBFCL to respond quickly when a fault occurs, limiting the fault current by increasing the impedance of the circuit, thereby protecting the DC transmission system from short-circuit faults. This design helps improve the safety and reliability of the system, especially in the face of grid faults.

[0066] Compared with the traditional BFCL, the improved MBFCL proposed in this embodiment reduces the isolation components, integrates the shunt branch and IGBT, and effectively reduces the system complexity and cost. Through the coordinated design of the shunt branch (RSH, LSH) and LDC, the rapid rise rate (di / dt) of the fault current is limited, and the protection capability of the IGBT and other key equipment is enhanced.

[0067] Compared with the traditional BFCL and superconducting current limiter (SCL), the improved MBFCL proposed in this embodiment avoids the use of complex materials and cooling systems, significantly reducing manufacturing and maintenance costs. It can adapt to various application scenarios such as high-voltage direct current transmission and large-scale distributed power generation, and meet the needs of different power levels and grid architectures.

[0068] Embodiment 2:

[0069] This embodiment provides a DC power transmission control method based on an improved bridge fault current limiter, comprising the following steps:

[0070] An improved bridge fault current limiter and a nonlinear controller as described in the first embodiment are arranged on each phase between the DC power source and the power grid, and the generator transmits power to the power grid through the improved bridge fault current limiter;

[0071] Nonlinear controllers such as Figure 2 As shown, the nonlinear controller takes the instantaneous phase voltage at the common coupling point (PCC) as or and delayed by a quarter cycle to produce a quadrature corresponding voltage Depend on Then With reference voltage V ref The voltage deviation ΔV of PCC is input into the nonlinear control module to generate the duty cycle d for the PWM module. The duty cycle d is defined as

[0072]

[0073] Among them, T c is the period of the PWM generator carrier, T off is the time when the MBFCL bridge IGBT is not conducting. c The definition of T c = DC power source T off +T on or T c =1 / f c , where T on is the conduction time of the MBFCL DC generator bridge IGBT, f c is the carrier frequency of the PWM generator.

[0074] Modified voltage This enables fast fault detection. The threshold voltage V th and The DC power source is compared to detect faults in the system. This signal is used for selectors in normal operation DC generator>DC generator V th When the IGBT gate is input with a signal value of 1, in any fault condition The inverted PWM generator output signal is input to the IGBT gate. During the entire fault period, MBFCL does not apply the full impedance value of the shunt path, but provides a variable effective shunt impedance value Z' to the system. shunt DC power source = d*Z shunt , for adaptive compensation, where Z shunt This adaptive compensation function enables MBFCL to be flexible and dynamically respond to the severity of the fault.

[0075] Due to the high degree of nonlinearity in the power system, a nonlinear controller is used to control the MBFCL. The nonlinear controller module takes ΔV as input and provides a duty cycle d to simulate the variable effective parallel impedance Z′ during a fault. shunt , the nonlinear function used is:

[0076] d=1-e -kΔV ;

[0077] Where d is the nonlinear calculation value, k is the adjustment coefficient, and ΔV is the deviation between the instantaneous phase voltage and the reference voltage.

[0078] The experimental results show that for all types and different strengths of faults, k DC generator = DC generator 20 has the best fault performance. Values ​​greater than this will lead to overcompensation, while values ​​less than this will lead to undercompensation. It shows the performance index value of the voltage deviation vlt (pu.s), defined as Here, the time from T0 to T of the DC generator is the integration time. Since this indicator measures the deviation of the PCC voltage, the smaller the value, the better the system performance. Figure 3 It can be seen that when the k value is greater than 20, no matter how the k value increases, the exponential value will increase and then remain at a fixed value. Similarly, when k < 20, the exponential value will increase as the k value decreases.

[0079] In other embodiments, the nonlinear function may also be a quadratic function, a cubic function, a logarithmic function, an exponential function, or the like.

[0080] Based on the above scheme, the nonlinear controller set in this embodiment monitors the voltage of the common coupling point (PCC) in real time to ensure the stable operation of the system. In the stable operation state, the IGBT in the MBFCL remains turned on, the shunt branch does not participate in the operation, and the system mainly relies on L DC Achieve preliminary regulation of the current change rate (di / dt) to reduce the dynamic stress on the IGBT.

[0081] When the grid is disturbed or faulty, causing abnormal current, the system enters fault response mode. At this time, the nonlinear control system quickly adjusts the shunt impedance of the MBFCL according to the PCC voltage deviation (ΔV). The MBFCL dynamically switches the IGBT and the R SH , L SH Working together, they effectively limit the growth of fault current to minimize the impact of grid disturbances.

[0082] Through the dynamic switching of the above two operating modes, this strategy achieves rapid response to power grid faults and effective protection of the power grid, improving the safety and stability of the system.

[0083] Embodiment three:

[0084] See also Figure 4 This embodiment proposes a DC power transmission control system based on an improved bridge fault current limiter, including:

[0085] A DC power source, an improved bridge fault current limiter as described in the first embodiment, and a nonlinear controller;

[0086] Each phase between the DC power source and the power grid is provided with an improved bridge fault current limiter and a nonlinear controller, and the generator transmits power to the power grid through the improved bridge fault current limiter;

[0087] The nonlinear controller monitors the instantaneous phase voltage at the common coupling point of the power grid in real time and detects power grid faults according to the instantaneous phase voltage;

[0088] When no grid fault is detected, the nonlinear controller sends a control signal with a signal value of 1 to the gate of the IGBT;

[0089] When a grid fault is detected, the nonlinear controller nonlinearly calculates the deviation between the instantaneous phase voltage and the reference voltage, outputs a nonlinear calculation value, generates a duty cycle according to the nonlinear calculation value, and outputs a PWM control signal to the gate of the IGBT through the PWM generator based on the duty cycle.

[0090] like Figure 4 As shown, Figure 4In the figure, the green block is the distributed DC generator (DG), the red block is the improved bridge fault current limiter and nonlinear controller of each phase, and the MBFCL is connected between the power grid and the DG system. A voltage-controlled converter (VSC) is also connected between the MBFCL and the power grid. The blue block is the controller, which provides gate pulses for the VSC.

[0091] The distributed DC generation source DG is connected to the improved bridge fault current limiter MBFCL, and the voltage-controlled converter VSC is responsible for converting the DC component into an AC component and connecting it to the grid through the MBFCL, thereby protecting the DG system by limiting the fault current. The power generated by the distributed DC generation source DG is transmitted to the grid by accurately adjusting the voltage-controlled converter. The reference DC voltage is compared with the calculated voltage, and the error is processed using a proportional integral controller (PI). The result of the PI controller is then fed back to the power exchange between the DG and the grid to generate the VSC reference power.

[0092] The distributed DC generator DG has an independent controller for regulating active power and reactive power, as well as detecting the DC voltage of the system. The entire controller operates through two main loops: an external controller that controls the DC voltage (Outer DC generator Voltage Controller) and an internal controller that controls the current (Inner DC generator Current Controller). DCsim ) and the reference DC voltage (V DCref ) is compared as Figure 5 This is controlled by a proportional integral controller (PI DC generator controller), whose value is the DC generator K p DC generator + DC generator K i / s.

[0093] DC voltage (V DC ) and DC current (I DC ) is the DC power (P DC The power provided by the voltage controller is the same as the DC power provided by the DC generator. DC The total power is added to the internal controller and becomes the reference power of the internal controller. ref ).like Figure 6 As shown, the internal controller consists of two parts, namely I d Controller and I q Controller. When the operation is in steady state, converting abc to dq gives the following formula:

[0094]

[0095] The active power and reactive power of the system can be expressed as follows

[0096]

[0097] Active power is determined by the direct axis current (I d ) is controlled, and the reactive power is controlled by the quadrature axis current (I q ) control. In this controller, the quadrature axis current (I q ) is set to 0, which means that the reactive power is controlled at unity power factor. The dq axis current component (i.e., the direct axis current I d and the quadrature axis current I q ) is converted again into three-phase current (abc) components, and then this three-phase current component is sent to the pulse width modulation (PWM) generator which injects the third harmonic.

[0098] Embodiment 4:

[0099] This embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, a DC power transmission control method based on an improved bridge fault current limiter as described in any embodiment of the present invention is implemented.

[0100] Embodiment five:

[0101] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the direct current transmission control method based on the improved bridge fault current limiter as described in any embodiment of the present invention is implemented.

[0102] In the embodiments of the present application, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent the existence of A alone, the existence of A and B at the same time, and the existence of B alone. Among them, A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b and c can be represented by: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, c can be single or multiple.

[0103] Those of ordinary skill in the art will appreciate that the various units and algorithm steps described in the embodiments disclosed herein can be implemented in a combination of electronic hardware, computer software, and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0104] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0105] In several embodiments provided in the present application, if any function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory; hereinafter referred to as: ROM), random access memory (Random Access Memory; hereinafter referred to as: RAM), disk or optical disk and other media that can store program codes.

[0106] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An improved bridge fault current limiter, characterized in that: include: A bridge current limiting circuit and a shunt branch arranged on a bridge arm of the bridge current limiting circuit; The shunt branch includes a first shunt circuit, a second shunt circuit and an IGBT; The first shunt circuit includes a first resistor and a first inductor connected in series, and the second shunt circuit includes a second resistor and a second inductor connected in series; The emitter and collector of the IGBT are connected in parallel with the second shunt circuit, and the gate of the IGBT is connected to the control unit; The parallel circuit of the second shunt circuit and the IGBT is connected in series with the first shunt circuit.

2. A DC power transmission control method based on an improved bridge fault current limiter, characterized in that: The following steps are involved: An improved bridge fault current limiter and a nonlinear controller as claimed in claim 1 are arranged in each phase between a DC power source and a power grid, and the generator transmits power to the power grid through the improved bridge fault current limiter; The nonlinear controller monitors the instantaneous phase voltage at the common coupling point of the power grid in real time and detects power grid faults according to the instantaneous phase voltage; When no grid fault is detected, the nonlinear controller sends a control signal with a signal value of 1 to the gate of the IGBT; When a grid fault is detected, the nonlinear controller nonlinearly calculates the deviation between the instantaneous phase voltage and the reference voltage, outputs a nonlinear calculation value, generates a duty cycle according to the nonlinear calculation value, and outputs a PWM control signal to the gate of the IGBT through the PWM generator based on the duty cycle.

3. A DC power transmission control method based on an improved bridge fault current limiter according to claim 2, characterized in that: The steps of detecting power grid faults according to instantaneous phase voltage are specifically as follows: Get the instantaneous phase voltage as V d,φ , for V d,φ A quarter-cycle delay produces a corresponding voltage V q,φ , calculate the comparison voltage according to the following formula: Among them, V dq,φ is the comparison voltage; V dq,φ With the preset voltage threshold V th Compare and determine whether the power grid has failed.

4. A DC power transmission control method based on an improved bridge fault current limiter according to claim 2, characterized in that: In the step of nonlinearly calculating the deviation between the instantaneous phase voltage and the reference voltage by the nonlinear controller, the nonlinear function used is: d=1-e -kΔV ; Where d is the nonlinear calculation value, k is the adjustment coefficient, and ΔV is the deviation between the instantaneous phase voltage and the reference voltage.

5. A DC power transmission control system based on an improved bridge fault current limiter, characterized in that: include: A DC power source, an improved bridge fault current limiter as claimed in claim 1, and a nonlinear controller; Each phase between the DC power source and the power grid is provided with an improved bridge fault current limiter and a nonlinear controller, and the generator transmits power to the power grid through the improved bridge fault current limiter; The nonlinear controller monitors the instantaneous phase voltage at the common coupling point of the power grid in real time and detects power grid faults according to the instantaneous phase voltage; When no grid fault is detected, the nonlinear controller sends a control signal with a signal value of 1 to the gate of the IGBT; When a grid fault is detected, the nonlinear controller nonlinearly calculates the deviation between the instantaneous phase voltage and the reference voltage, outputs a nonlinear calculation value, generates a duty cycle according to the nonlinear calculation value, and outputs a PWM control signal to the gate of the IGBT through the PWM generator based on the duty cycle.

6. A DC power transmission control system based on an improved bridge fault current limiter according to claim 5, characterized in that: The steps of the nonlinear controller detecting a power grid fault according to the instantaneous phase voltage are specifically as follows: Get the instantaneous phase voltage as V d,φ , for V d,φ A quarter-cycle delay produces a corresponding voltage V q,φ , calculate the comparison voltage according to the following formula: Among them, V dq,φ is the comparison voltage; V dq,φ With the preset voltage threshold V th Compare and determine whether the power grid has failed.

7. A DC power transmission control system based on an improved bridge fault current limiter according to claim 5, characterized in that: In the step of nonlinearly calculating the deviation between the instantaneous phase voltage and the reference voltage by the nonlinear controller, the nonlinear function used is: d=1-e -kΔV ; Where d is the nonlinear calculation value, k is the adjustment coefficient, and ΔV is the deviation between the instantaneous phase voltage and the reference voltage.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the direct current transmission control method based on the improved bridge fault current limiter as claimed in any one of claims 2 to 4 is implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the direct current transmission control method based on the improved bridge fault current limiter as claimed in any one of claims 2 to 4 is implemented.

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