Fault stability control method and system for converter of offshore hvdc grid-connected type receiving end

Abstract

The application provides a kind of kind of sea wind straight netting type fault stability control method and system of receiving end converter, comprising: inertia adjustment-based power angle stability control strategy, under power grid fault, switch the synchronous link based on direct current voltage to the synchronous link based on active power, and set virtual inertia, for reducing the power angle increasing speed of receiving end converter, to improve the power angle stability of receiving end converter;Current limiting strategy based on adaptive virtual impedance, in steady state, put in an adaptive virtual impedance, when fault current exceeds the limiting value, according to the size of fault current, the amplitude of virtual impedance is dynamically adjusted, for inhibiting the periodic component of fault current;At the same time, according to the peak value of fault current, introduce nonlinear resistance, for inhibiting the decay component of fault current.The application realizes the power grid fault stability safety crossing of network type receiving end converter by inertia adjustment-based power angle stability control and current limiting based on adaptive virtual impedance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power grid, in particular to a fault stability control method and system for a sea wind flexible network type receiving end converter, and relates to a corresponding computer terminal and computer readable storage medium. BACKGROUND

[0002] In recent years, with the large-scale development of offshore wind power, the replacement of wind power-flexible direct current grid-connected system without inertia reduces the overall inertia of the power grid, and under the background that the single set capacity of offshore wind power-flexible direct current system has reached GW level, it will seriously affect the frequency stability of power grid operation. On the other hand, with the increasing proportion of renewable energy in the power grid, the power grid is becoming weaker, and when the short-circuit ratio of the wind power-flexible direct current system grid-connected point is low, the phase-locked loop dynamic performance of the receiving end converter is poor, and it is easy to appear oscillation instability phenomenon. Under the control of current source type, the wind power-flexible direct current system cannot become the dominant power supply, which limits the further improvement of its grid-connected capacity. If a new energy system dominated by wind and solar power is to be built, the wind power-flexible direct current system needs to change from a following type power supply to a dominant type power supply, to a certain extent, like a synchronous generator, to undertake the obligation of establishing power system voltage and maintaining system real-time energy balance, and voltage source type control is a powerful means to achieve this goal.

[0003] Because the onshore alternating current main grid usually uses overhead lines for transmission, ground fault is common. After the fault occurs, the receiving end converter needs to limit the output current, and when the current type control is adopted, the receiving end converter can limit the output current through the grid-connected point voltage feedforward and the fast control of the current inner loop. However, for the receiving end converter under voltage source type control, current limiting is a big technical difficulty. Similar to the synchronous generator, the receiving end converter controlled by voltage source, when the power grid fails, also has the problem of synchronous stability. And the power angle characteristic of the receiving end converter will also be limited by the overcurrent capacity of the power electronic device, and the power angle instability problem is easy to occur under serious power grid fault. SUMMARY

[0004] The present application provides a fault stability control method and system for a sea wind flexible network type receiving end converter, and a corresponding computer terminal and computer readable storage medium.

[0005] According to one aspect of the present application, a fault stability control method for a sea wind flexible network type receiving end converter is provided, comprising: an inertia-adjusted power angle stability control strategy and a current limiting strategy based on adaptive virtual impedance; wherein:

[0006] The power angle stabilization control strategy based on inertia adjustment switches the synchronization link based on DC voltage to the synchronization link based on active power under grid fault conditions, and sets virtual inertia to reduce the power angle acceleration of the receiving-end converter, thereby improving the power angle stability of the receiving-end converter.

[0007] The current limiting strategy based on adaptive virtual impedance introduces an adaptive virtual impedance in steady state. When the fault current exceeds the limit value, the amplitude of the virtual impedance is dynamically adjusted according to the magnitude of the fault current to suppress the periodic component of the fault current. At the same time, a nonlinear virtual resistor is introduced according to the peak value of the fault current to suppress the attenuation component of the fault current.

[0008] Preferably, during the control process of the receiving-end converter, flag is set as a signal bit, U dc This is a DC voltage measurement value, U dc_nom The rated DC voltage, ω nom The frequency is the rated frequency, K is the coupling coefficient, and ω is the ω value. rec Q is the output frequency of the receiving-end converter, θ is the output phase of the receiving-end converter, and Q is the output frequency of the receiving-end converter. ref U is the reactive power setpoint of the receiving-end converter, Q is the measured reactive power value of the receiving-end converter, and U is the reactive power value of the receiving-end converter. ref The given value of the AC output voltage of the receiving-end converter is M, where M is the damping coefficient and ΔU is the damping voltage. rec P is the AC output voltage of the receiving-end converter. ref For the active power reference during a fault in the receiving-end converter, P is the output active power of the receiving-end converter, and U is the active power reference during a fault in the receiving-end converter. abcf is the fault limiting voltage; J is the virtual inertia coefficient, D is the virtual damping coefficient, and s is the Laplace operator;

[0009] The above describes the receiving-end converter operating in steady state, with flag = 0. In this case, a synchronization mechanism based on DC voltage is used, controlled by U. dc and U dc_nom After taking the difference, multiply by ω nom Divide by K and U dc_nom , plus ω nom Obtain the output frequency ω rec The output phase θ is obtained by integrating the results; simultaneously, Q is used to obtain the output phase θ. ref The difference between Q and the reactive power controller is applied, followed by a damped voltage ΔU. ΔU then passes through U. dc and U dc_nom The difference is obtained by multiplying by M, and then the output AC voltage U is finally calculated. ref And by θ and U rec Generate the initial value U of the three-phase reference AC voltage of the receiving-end converter. s In steady state, since flag = 0, the final value of the three-phase reference voltage U is... abcf equal to Us .

[0010] Preferably, the inertia-based regulation-based power angle stability control strategy comprises:

[0011] After detecting the power grid fault, the flag is set to 1, at which time the active power-based synchronization link is adopted, and a virtual inertia is set, and the frequency calculation path is changed, at which time the output frequency ω of the receiving converter rec is equal to the difference between P ref and P divided by Js+D, plus ω nom ; the size of P ref and the value of J are adjusted according to the fault depth, wherein the size of P ref is smaller when the fault is more serious, and the value of J is larger when the fault is more serious, so as to slow down the power angle change speed of the converter and avoid the problem of power angle instability.

[0012] Preferably, the current limiting strategy based on adaptive virtual impedance comprises:

[0013] Under fault, the initial value of the three-phase reference AC voltage U s of the converter is subtracted by the fault current limiting voltage U abcf , to obtain the final three-phase reference AC voltage U abc_ref ; by increasing the size of the virtual reactance, the fault current limiting voltage U abcf is increased; by reducing the three-phase reference AC voltage U abc_ref , the fault current is reduced. Wherein:

[0014] The calculation method of U abcf is:

[0015] i o is the output current of the receiving converter, i o is subjected to PARK transformation at the output phase θ of the receiving converter to obtain the dq-axis components i d and i q of the output current, i d and i q are multiplied by the virtual resistance R v and the virtual reactance L v respectively and combined to obtain the dq-axis components u d and u q of the fault current limiting voltage, and u d and u q are subjected to inverse PARK transformation at the output phase θ of the receiving converter to obtain the three-phase reference value U abcf of the fault current limiting voltage.

[0016] The value of L v is:

[0017] i d i q square root of the sum of squares of i lim , which is generally 1.2-1.5 times of the rated current, through a proportional-integral link to obtain the value of virtual reactance L v .

[0018] The value of R v is:

[0019] R v = K v (I oT -I lim )

[0020] In the formula, I oT is the instantaneous maximum value of the converter output current, K v is a transient voltage suppression coefficient, and the value range is 1-10, and I lim is the fault current clipping value.

[0021] According to another aspect of the present application, a fault stability control method of a sea wind HVDC grid-type receiving-end converter is provided, comprising: an inertia regulation-based power angle stability control module and a current clipping module based on adaptive virtual impedance; wherein:

[0022] The inertia regulation-based power angle stability control module switches the DC voltage-based synchronization link to an active power-based synchronization link under grid fault, and sets a virtual inertia for reducing the power angle increasing rate of the receiving-end converter and improving the power angle stability of the receiving-end converter;

[0023] The current clipping module based on adaptive virtual impedance inputs an adaptive virtual impedance in the steady state, dynamically adjusts the amplitude of the virtual impedance according to the size of the fault current when the fault current exceeds the clipping value, and is used for suppressing the periodic component of the fault current; at the same time, a nonlinear virtual resistance is introduced according to the peak value of the fault current, which is used for suppressing the decay component of the fault current.

[0024] According to a third aspect of the present application, a computer terminal is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to execute the method of any one of the above aspects of the present application, or runs the system described in the above aspects of the present application.

[0025] According to a fourth aspect of the present application, a computer readable storage medium is provided, which stores a computer program executable by a processor to execute the method of any one of the above aspects of the present application, or to run the system described in the above aspects of the present application.

[0026] Compared with the prior art, the application has at least one of the following beneficial effects:

[0027] The application provides a fault stability control method and system for a sea wind flexible straight grid type receiving end converter, and proposes an inertia regulation based power angle stability control technology, so that the grid type receiving end converter can be automatically switched from a synchronous mode based on DC voltage to a synchronous mode based on active power when a power grid fails, and the power angle increasing speed of the converter is slowed down through setting of large inertia, and the power grid failure power angle stability of the grid type receiving end converter is improved.

[0028] The application provides a fault stability control method and system for a sea wind flexible straight grid type receiving end converter, and proposes an inertia regulation based power angle stability control technology, so that the grid type receiving end converter can be automatically switched from a synchronous mode based on DC voltage to a synchronous mode based on active power when a power grid fails, and the power angle increasing speed of the converter is slowed down through setting of large inertia, and the power grid failure power angle stability of the grid type receiving end converter is improved.

[0029] The application provides a fault stability control method and system for a sea wind flexible straight grid type receiving end converter, and proposes an inertia regulation based power angle stability control technology, so that the grid type receiving end converter can be automatically switched from a synchronous mode based on DC voltage to a synchronous mode based on active power when a power grid fails, and the power angle increasing speed of the converter is slowed down through setting of large inertia, and the power grid failure power angle stability of the grid type receiving end converter is improved. BRIEF DESCRIPTION OF DRAWINGS

[0030] Other features, objects and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0031] Figure 1 The figure is a working schematic diagram of a fault stability control method for a sea wind flexible straight grid type receiving end converter in an embodiment of the application.

[0032] Figure 2 The figure is a structure schematic diagram of an offshore wind power-flexible HVDC power grid system in a preferred embodiment of the application.

[0033] Figure 3 The figure is a working schematic diagram of a steady state grid connection strategy of a receiving end converter in a preferred embodiment of the application.

[0034] Figure 4 The figure is a working schematic diagram of a limiting method based on virtual impedance in a preferred embodiment of the application.

[0035] Figure 5 The figure is a working schematic diagram of a virtual impedance value determination method in a preferred embodiment of the application.

[0036] Figure 6The following is a simulation verification result of fault ride-through in a verification example of the present invention; wherein, (a) is the AC voltage at the grid connection point of the flexible DC receiving-end converter during the fault, (b) is the output AC current of the flexible DC receiving-end converter during the fault, (c) is the output active power and reactive power at the grid connection point of the flexible DC receiving-end converter during the fault, and (d) is the DC voltage of the flexible DC system during the fault; the horizontal axis in the figure represents time.

[0037] Figure 7 This is a schematic diagram of the components of the fault stability control system of the offshore flexible DC grid-type receiving-end converter in one embodiment of the present invention. Detailed Implementation

[0038] The embodiments of the present invention are described in detail below: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

[0039] In existing technologies, grid-type receiving-end converters in offshore flexible DC systems typically employ DC voltage synchronous control. This control method lacks grid fault ride-through capability, resulting in poor grid fault ride-through performance and susceptibility to overcurrent and power angle instability. To address these issues, one embodiment of the present invention provides a fault stability control method for offshore flexible DC grid-type receiving-end converters. This method employs a power angle stability control strategy based on inertia adjustment to slow down the power angle acceleration of the receiving-end converter, thereby enhancing its power angle stability. Furthermore, it uses a current limiting strategy based on adaptive virtual impedance to suppress the periodic and attenuation components of the fault current.

[0040] Specifically, such as Figure 1 As shown, the fault stability control method for the offshore flexible DC grid-type receiving-end converter provided in this embodiment may include: a power angle stability control strategy based on inertia adjustment and a current limiting strategy based on adaptive virtual impedance; wherein:

[0041] The power angle stabilization control strategy based on inertia regulation switches the synchronization link based on DC voltage to the synchronization link based on active power under grid fault conditions, and sets a larger virtual inertia (i.e., virtual inertia coefficient J) to slow down the power angle increase of the receiving-end converter and enhance the power angle stability of the receiving-end converter.

[0042] The current limiting strategy based on adaptive virtual impedance sets an adaptive virtual impedance (i.e., virtual resistance R). v and virtual reactance L vIn steady state, a small virtual impedance is applied. When the fault current exceeds the limit, the amplitude of the virtual impedance is dynamically adjusted according to the magnitude of the fault current to suppress the periodic component of the fault current. Simultaneously, a nonlinear virtual resistance (i.e., virtual resistance R) is introduced based on the peak value of the fault current. v ), used to suppress the attenuation component of fault current.

[0043] The preferred technical solution of the fault stability control method for the offshore flexible direct current grid-type receiving-end converter provided in this embodiment will be further described in detail below with reference to the accompanying drawings.

[0044] like Figure 2 The diagram shown is a structural schematic of an offshore wind power-flexible DC transmission grid-connected system. The fault stability control method provided in the above embodiments of the present invention mainly controls the onshore receiving-end converter.

[0045] like Figure 3 The diagram shows the control strategy for the receiving-end converter. Figure 3 In the text, flag is a signal bit, U dc This is a DC voltage measurement value, U dc_nom The rated DC voltage, ω nom The frequency is the rated frequency, K is the coupling coefficient, and ω is the ω value. rec Q is the output frequency of the receiving-end converter, θ is the output phase of the receiving-end converter, and Q is the output frequency of the receiving-end converter. ref U is the reactive power setpoint of the receiving-end converter, Q is the measured reactive power of the receiving-end converter, and the reactive power controller can preferably use a proportional element or a proportional / integral element. ref The given value of the AC output voltage of the receiving-end converter is M, where M is the damping coefficient and ΔU is the damping voltage. rec P is the AC output voltage of the receiving-end converter. ref For the active power reference during a fault in the receiving-end converter, P is the output active power of the receiving-end converter, and U is the active power reference during a fault in the receiving-end converter. abcf The fault limiting voltage is denoted by J. J is the virtual inertia coefficient, D is the virtual damping coefficient, and s is the Laplace operator.

[0046] During steady-state operation, flag = 0. In this case, a synchronization mechanism based on DC voltage is used, controlled by U. dc and U dc_nom After taking the difference, multiply by ω nom Divide by K and U dc_nom , plus ω nom Obtain the output frequency ω rec And integrate to obtain the output phase θ. Simultaneously, through Q... ref The difference between Q and the reactive power controller is applied, followed by a damping voltage ΔU. More preferably, ΔU is applied through U... dc and U dc_nomAfter the difference is obtained, multiply by M to obtain, and finally calculate the output AC voltage U ref , and by θ and U rec Generate the initial value of the three-phase reference AC voltage of the receiving end converter U s , and the final value of the three-phase reference voltage U abcf equals U s .

[0047] In some preferred embodiments, the inertia-based regulation-based power angle stability control strategy comprises:

[0048] After detecting a grid fault, flag is set to 1, at which time the active power-based synchronization link is adopted, and a virtual inertia is set, and the frequency calculation path changes, at which time the output frequency ω rec of the converter equals the difference between P ref and P divided by Js+D, plus ω nom . The size of P ref may be adjusted according to the fault depth, and P ref should be smaller when the fault is more serious. The value of J can also be adjusted according to the fault depth, and J is larger when the fault is more serious, so as to slow down the power angle change speed of the converter and avoid power angle instability problems.

[0049] In some preferred embodiments, the current limiting strategy based on adaptive virtual impedance comprises:

[0050] Under a fault, the initial value of the three-phase reference AC voltage of the converter U s is subtracted from the fault current limiting voltage U abcf to obtain the final three-phase reference AC voltage U abc_ref . By increasing the size of the virtual reactance, the fault current limiting voltage U abcf is increased; by reducing the three-phase reference AC voltage U abc_ref , the fault current is reduced. As shown in Figure 5 .

[0051] In some preferred embodiments, the calculation of U abcf is as shown in Figure 4 , and can further comprise:

[0052] i o is the output current of the receiving end converter, i o is subjected to PARK transformation at the output phase θ of the receiving end converter to obtain the dq-axis components i d and i q of the output current, i d and i q are respectively multiplied by the virtual resistance R v and the virtual reactance L vAfter multiplication and combination, the dq-axis component u of the fault limiting voltage is obtained. d with u q Then u d with u q An inverse PARK transformation is performed at the output phase θ of the receiving-end converter to obtain the three-phase reference value U of the fault limiting voltage. abcf .

[0053] In some preferred embodiments, the virtual resistance R v and virtual reactance L v The value will be adjusted in real time according to the output AC current.

[0054] In a further preferred embodiment, L v The values ​​are as follows Figure 5 As shown, it may further include:

[0055] will i d with i q The square root of the sum of squares, minus the current limiting value i. lim The value is generally preferred to be 1.2 to 1.5 times the rated current. After passing through a proportional-integral circuit, the virtual reactance L is obtained. v The value of .

[0056] In a further preferred embodiment, R v The value of can be further shown in the following formula:

[0057] R v =K v (I oT -I lim )

[0058] In the formula, I oT K represents the instantaneous maximum value of the converter output current. v I is the transient voltage suppression coefficient, with a value ranging from 1 to 10. lim This is the fault current limit value.

[0059] The performance of the fault stability control method provided in the above embodiments of the present invention will be illustrated below through a verification example.

[0060] Create such in PSCAD / EMTDC Figure 2 The simulation model of the system shown below has the following system parameters:

[0061] Parameter name Value Rated active power / MW 1100 Rated grid voltage / kV 500 Rated voltage on wind farm side / kV 220 Rated DC voltage / kV ±400 Number of submodules per bridge leg 400 + 50 (redundancy) Submodule capacitance / mF 11 Bridge leg reactance / mH 150 Coupling transformer capacity / MVA 1400 Coupling transformer leakage reactance / p.u. 0.14 Converter 1 transformer ratio 416 / 500 Converter 2 transformer ratio 416 / 220

[0062] The wind farm has an output power of 800MW. At t=0.5s, a three-phase ground fault occurs in the power grid. At this time, the grid frequency, the DC voltage difference between the sending end and the negative end, and the wind farm frequency are as follows: Figure 6As shown, it can be found that the grid frequency can be well mirrored into the offshore wind farm through the positive and negative DC voltage difference.

[0063] An embodiment of the present application provides a fault stability control system of a sea wind flexible network type receiving end converter, which comprises a power angle stability control module based on inertia adjustment and a current limiting module based on adaptive virtual impedance. Figure 7 As shown, the power angle stability control module based on inertia adjustment and the current limiting module based on adaptive virtual impedance can be included, wherein:

[0064] The power angle stability control module based on inertia adjustment switches the DC voltage-based synchronization link into an active power-based synchronization link under grid fault, and sets a large virtual inertia for slowing down the power angle increasing speed of the receiving end converter and enhancing the power angle stability of the receiving end converter.

[0065] The current limiting module based on adaptive virtual impedance sets adaptive virtual impedance, inputs a small virtual impedance in a steady state, dynamically adjusts the amplitude of the virtual impedance according to the size of the fault current when the fault current exceeds the limiting value, and is used for suppressing the periodic component of the fault current; meanwhile, a nonlinear virtual resistance is introduced according to the peak value of the fault current, and is used for suppressing the decay component of the fault current.

[0066] It should be noted that the steps in the method provided by the present application can be realized by corresponding modules, devices, units and the like in the system, and those skilled in the art can refer to the technical scheme of the method to realize the composition of the system, that is, the embodiments in the method can be understood as preferred examples of constructing the system, and details are not described herein.

[0067] An embodiment of the present application provides a computer terminal, which comprises a memory, a processor and a computer program stored in the memory and capable of running on the processor, and the processor can be used to execute the method of any one of the above-mentioned embodiments of the present application or run the system of any one of the above-mentioned embodiments of the present application when executing the computer program.

[0068] Optionally, a memory is configured to store a program; the memory can include volatile memory (e.g., random-access memory (RAM), such as static random-access memory (SRAM), Double Data Rate Synchronous Dynamic Random Access Memory (DDR SDRAM), etc.), and / or non-volatile memory (e.g., flash memory). The memory is configured to store computer programs (e.g., application programs, functional modules, etc. for implementing the above-described methods), computer instructions, etc. The computer programs, computer instructions, etc. described above can be stored in one or more memories in a partitioned manner. Furthermore, the computer programs, computer instructions, data, etc. described above can be invoked by the processor.

[0069] The computer programs, computer instructions, etc. described above can be stored in one or more memories in a partitioned manner. Furthermore, the computer programs, computer instructions, data, etc. described above can be invoked by the processor.

[0070] The processor is configured to execute the computer programs stored in the memory, so as to implement the various steps in the methods or the various modules of the system according to the above-described embodiments. For details, refer to the related descriptions in the above method and system embodiments.

[0071] The processor and the memory can be independent structures, or can be integrated into an integrated structure. When the processor and the memory are independent structures, the memory and the processor can be coupled and connected through a bus.

[0072] An embodiment of the present application provides a computer readable storage medium, which stores a computer program. The computer program is executed by a processor, so as to implement the method according to any one of the above-described embodiments of the present application, or run the system according to any one of the above-described embodiments of the present application.

[0073] The fault stability control method and system of the sea wind flexible network type receiving end converter provided by the above embodiments of the present application propose an inertia regulation based power angle stability control technology, so that the network type receiving end converter can automatically switch from the direct current voltage based synchronization mode to the active power based synchronization mode when the power grid fails, and the inertia regulation slows down the power angle increase of the converter, thereby improving the power grid failure power angle stability of the network type receiving end converter; a current limiting technology based on adaptive virtual impedance is proposed, an adaptive virtual impedance is connected during the failure to ensure that the periodic component of the failure current output by the network type receiving end converter does not exceed the limit, and a nonlinear virtual resistance is connected at the moment of the failure to ensure that the instantaneous component of the failure current output by the network type receiving end converter does not exceed the limit; through the inertia regulation based power angle stability control technology and the current limiting technology based on adaptive virtual impedance, the network type receiving end converter can stably and safely pass through the power grid failure.

[0074] The above embodiments of the present application are described. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or changes within the scope of the claims, which does not affect the essential content of the present application.

[0075] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or changes within the scope of the claims, which does not affect the essential content of the present application.

Claims

1. A fault stability control method for a sea-wind flexible DC grid-type receiving-end converter, characterized in that, include: A power angle stabilization control strategy based on inertia regulation and a current limiting strategy based on adaptive virtual impedance; wherein: The power angle stabilization control strategy based on inertia adjustment switches the synchronization link based on DC voltage to the synchronization link based on active power under grid fault conditions, and sets virtual inertia to reduce the power angle acceleration of the receiving-end converter, thereby improving the power angle stability of the receiving-end converter. The current limiting strategy based on adaptive virtual impedance dynamically adjusts the magnitude of the virtual impedance according to the magnitude of the fault current when the fault current exceeds the limit value, in order to suppress the periodic component of the fault current; at the same time, a nonlinear virtual resistor is introduced according to the peak value of the fault current to suppress the attenuation component of the fault current. In the control process of the receiving-end converter, let flag be a signal bit, U dc This is a DC voltage measurement value, U dc_nom The rated DC voltage, ω nom Where ω is the rated frequency, K is the coupling coefficient, and ω is the frequency. rec Q is the output frequency of the receiving-end converter, θ is the output phase of the receiving-end converter, and Q is the output frequency of the receiving-end converter. ref U is the reactive power setpoint of the receiving-end converter, Q is the measured reactive power value of the receiving-end converter, and U is the reactive power value of the receiving-end converter. ref The given value of the AC output voltage of the receiving-end converter is M, where M is the damping coefficient and ΔU is the damping voltage. rec P is the AC output voltage of the receiving-end converter. ref For the active power reference during a fault in the receiving-end converter, P is the output active power of the receiving-end converter, and U is the active power reference during a fault in the receiving-end converter. abcf is the fault limiting voltage; J is the virtual inertia coefficient, D is the virtual damping coefficient, and s is the Laplace operator; When the receiving-end converter is operating in steady state, flag = 0. At this time, a synchronization link based on DC voltage is used, controlled by U. dc and U dc_nom After taking the difference, multiply by ω nom Divide by K and U dc_nom The product of , plus ω nom Obtain the output frequency ω of the receiving-end converter rec The output phase θ of the receiving-end converter is obtained by integration; simultaneously, through Q... ref The difference between Q and the output AC voltage U of the receiving-end converter is calculated by passing the reactive power controller and then applying the damping voltage ΔU. rec And by θ and U rec Generate the initial value U of the three-phase reference AC voltage of the receiving-end converter. s In steady state, since flag = 0, the final three-phase reference AC voltage U is... abc_ref equal to U s .

2. The fault stability control method for the offshore flexible DC grid-type receiving-end converter according to claim 1, characterized in that, It also includes any one or more of the following: -The reactive power controller adopts a proportional element or a proportional / integral element; -The ΔU is through U dc_nom and U dc The result is obtained by multiplying the difference by M.

3. The fault stability control method for the offshore flexible DC grid-type receiving-end converter according to claim 1, characterized in that, The power angle stabilization control strategy based on inertia regulation includes: When a grid fault is detected, flag is set to 1. At this time, a synchronization link based on active power is adopted, and a virtual inertia is set. The frequency calculation path changes, and the output frequency ω of the receiving-end converter changes accordingly. rec equals P ref Divide the difference between P and (Js+D), and add ω nom Adjust P according to the fault depth ref The magnitude of the value and the value of J are determined to reduce the rate of change of the converter's power angle and avoid power angle instability.

4. The fault stability control method for the offshore flexible DC grid-type receiving-end converter according to claim 1, characterized in that, The current limiting strategy based on adaptive virtual impedance includes: Under fault conditions, the initial value U of the three-phase reference AC voltage of the receiving-end converter is... s Subtract the fault limiting voltage U abcf Obtain the final three-phase reference AC voltage U abc_ref Virtual impedance includes virtual resistance and virtual reactance. By increasing the magnitude of virtual reactance, the fault limiting voltage U can be increased. abcf By reducing the three-phase reference AC voltage U abc_ref This reduces the fault current.

5. The fault stability control method for the offshore flexible DC grid-type receiving-end converter according to claim 4, characterized in that, The U abcf The calculation methods include: i o For the output current of the receiving-end converter, i o Performing PARK transformation at the output phase θ of the receiving-end converter yields the dq-axis component i of the output current. d with i q , through (i d ×R v )-(i q ×ω nom L v ), to obtain the d-axis component u of the fault limiting voltage. d , through (i q ×R v )+(i d ×ω nom L v ), to obtain the q-axis component u of the fault limiting voltage. q Then u d with u q Perform inverse PARK transformation at the output phase θ of the receiving-end converter to obtain the fault limiting voltage U. abcf Among them, R v For virtual resistance, L v For virtual reactance, ω nom L v Represents ω nom and L v The product of.

6. The fault stability control method for a marine flexible DC grid-type receiving-end converter according to claim 5, characterized in that, The virtual resistance R v and the virtual reactance L v The value is adjusted in real time according to the output AC current; where: The L v The methods for obtaining values ​​include: will i d with i q The square root of the sum of squares, minus the current limiting value i. lim After a proportional-integral process, the virtual reactance L is obtained. v The value; The R v The value can be: R v =K v (I oT -I lim ) In the formula, I oT K represents the instantaneous maximum value of the converter output current. v I is the transient voltage suppression coefficient, with a value ranging from 1 to 10. lim This is the fault current limit value.

7. A fault stability control system for a marine-style flexible DC grid-connected receiving-end converter, characterized in that, include: A power angle stabilization control module based on inertia regulation and a current limiting module based on adaptive virtual impedance; wherein: The inertia-based power angle stabilization control module switches the DC voltage-based synchronization link to the active power-based synchronization link under grid fault conditions, and sets a virtual inertia to reduce the power angle acceleration of the receiving-end converter and improve the power angle stability of the receiving-end converter. The current limiting module based on adaptive virtual impedance dynamically adjusts the amplitude of the virtual impedance according to the magnitude of the fault current when the fault current exceeds the limit value, in order to suppress the periodic component of the fault current; at the same time, a nonlinear virtual resistor is introduced according to the peak value of the fault current to suppress the attenuation component of the fault current. In the control process of the receiving-end converter, let flag be a signal bit, U dc This is a DC voltage measurement value, U dc_nom The rated DC voltage, ω nom Where ω is the rated frequency, K is the coupling coefficient, and ω is the frequency. rec Q is the output frequency of the receiving-end converter, θ is the output phase of the receiving-end converter, and Q is the output frequency of the receiving-end converter. ref U is the reactive power setpoint of the receiving-end converter, Q is the measured reactive power value of the receiving-end converter, and U is the reactive power value of the receiving-end converter. ref The given value of the AC output voltage of the receiving-end converter is M, where M is the damping coefficient and ΔU is the damping voltage. rec P is the AC output voltage of the receiving-end converter. ref For the active power reference during a fault in the receiving-end converter, P is the output active power of the receiving-end converter, and U is the active power reference during a fault in the receiving-end converter. abcf is the fault limiting voltage; J is the virtual inertia coefficient, D is the virtual damping coefficient, and s is the Laplace operator; When the receiving-end converter is operating in steady state, flag = 0. At this time, a synchronization link based on DC voltage is used, controlled by U. dc and U dc_nom After taking the difference, multiply by ω nom Divide by K and U dc_nom The product of , plus ω nom Obtain the output frequency ω of the receiving-end converter rec The output phase θ of the receiving-end converter is obtained by integration; simultaneously, through Q... ref The difference between Q and the output AC voltage U of the receiving-end converter is calculated by passing the reactive power controller and then applying the damping voltage ΔU. rec And by θ and U rec Generate the initial value U of the three-phase reference AC voltage of the receiving-end converter. s In steady state, since flag = 0, the final three-phase reference AC voltage U is... abc_ref equal to U s .

8. A computer terminal, 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 computer program, it can be used to perform the method of any one of claims 1-6, or to run the system of claim 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program can be used to perform the method of any one of claims 1-6, or to run the system of claim 7.

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