Low voltage ride through and recovery method for grid-forming converters and related apparatus

Abstract

The application discloses a low-voltage ride-through and recovery method of grid-forming converter and related devices, and relates to the technical field of power electronics. The method comprises the following steps: sampling the actual current of a power grid, obtaining a virtual impedance value in combination with a reactive current injection reference value and an active current injection reference value, obtaining a voltage amplitude compensation amount after determining a voltage drop value generated by the virtual impedance value; obtaining a secondary corrected voltage amplitude instruction according to the voltage amplitude compensation amount and a primary corrected voltage amplitude instruction; controlling the low-voltage ride-through of the grid-forming converter through the corrected angular frequency instruction and the secondary corrected voltage amplitude instruction, and performing smooth correction on the virtual impedance value and a power loop reference value after detecting a fault recovery instruction, so as to control the grid-forming converter to smoothly exit the fault ride-through state. The application can solve the problem of how to avoid current impact of the grid-forming converter in the process of power grid voltage drop fault and fault recovery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a low-voltage ride-through and recovery method of grid-forming converter and related devices. BACKGROUND

[0002] At present, the low-carbon transformation of energy is accelerating, and the energy transformation mainly relies on expanding the proportion of clean energy, low-carbon energy and zero-carbon energy, and promoting the realization of energy production and consumption mode centered on electricity. New energy replacing traditional energy is an inevitable trend of development, and new energy generation as the main body should have the corresponding characteristics of synchronous machines, and bear the support and support of the power grid. The rapid development of new energy construction forces the power grid to realize efficient interaction with it. In the new energy high penetration rate power system, with the increasing proportion of power electronic converters in the power system, the traditional power grid dominated by synchronous generators is changing. The corresponding converter in the power system is increasing, making the new power system (i.e. microgrid system) present the characteristics of "double high" of high proportion of renewable energy and high proportion of power electronic equipment, the system inertia is greatly reduced, the system frequency index is deteriorated, and the power grid lacks inertia support, making the voltage and frequency stability of the new power system face challenges. The grid-forming control technology does not rely on phase-locked loop and power grid for synchronization, and can provide voltage support for the whole process of the power grid, and can solve the voltage and frequency stability problem of the new power system, and realize active perception, active response and active support of the power grid.

[0003] As shown in Figure 2 Since the grid-forming grid-connected inverter has the inherent characteristics of a voltage source, its output voltage is not affected by power grid faults. Therefore, after the power grid fails, the output current of the grid-forming grid-connected inverter will increase rapidly, triggering the overcurrent protection and causing the new energy generator set to be off-grid, which will seriously collapse the entire system and endanger the stable operation of the system. In order to improve the stability of the new power system dominated by new energy, when the power grid has a short-time fault, the new energy generator set must remain on-grid operation. Therefore, when the power grid fails, the fault current of the grid-forming grid-connected inverter must be limited to ensure that the new energy generator set remains on-grid operation. In addition, the grid-connected inverter should have low-voltage ride-through capability, that is, the grid-connected inverter needs to inject a certain amount of reactive current into the power grid within 30ms after the power grid voltage drops to help the power grid recover. However, due to the narrow bandwidth and slow response speed of the power of the grid-forming grid-connected inverter power outer loop, the reactive current regulation speed of the grid-forming grid-connected inverter is slow, which may cause low-voltage ride-through failure. Therefore, the grid-forming grid-connected inverter realizes the limitation of fault current and the rapid injection of reactive current during power grid failure, which is the key to the reliable operation of the new power system dominated by new energy.

[0004] The grid-forming converter in the micro-grid can build voltage and frequency autonomously. When the grid voltage drops, the grid-forming converter will automatically inject a large current when it is connected to the grid, which will deteriorate the power quality, damage fragile equipment, and even cause the system to be offline. At the same time, when the grid voltage drops, the grid-forming converter needs to inject reactive current to the grid according to the grid voltage drop to help the grid recover. Therefore, how to avoid the current impact and rapid injection of reactive power of the grid-forming converter under the grid voltage drop fault needs to be solved. SUMMARY

[0005] The purpose of the present application is to provide a low voltage ride through and recovery method and related device of grid-forming converter, to solve the problem of how to avoid the current impact of grid-forming converter in the process of grid voltage drop fault and fault recovery.

[0006] To achieve the above purpose, the present application adopts the following technical scheme:

[0007] In a first aspect, a low voltage ride through and recovery method of grid-forming converter, comprising the following steps:

[0008] Obtain the reactive current injection reference value and the active current injection reference value of the grid-forming converter, and calculate the power ring reference value of the droop control power ring low voltage ride through according to the reactive current injection reference value and the active current injection reference value, and modify the angular frequency instruction and the voltage amplitude instruction of the grid-forming converter according to the power ring reference value, to obtain the modified angular frequency instruction and the first modified voltage amplitude instruction;

[0009] Sample the actual current of the grid, and obtain the virtual impedance value by combining the reactive current injection reference value and the active current injection reference value, and obtain the voltage amplitude compensation amount after determining the voltage drop value corresponding to the virtual impedance value;

[0010] Modify the first modified voltage amplitude instruction according to the voltage amplitude compensation amount to obtain the second modified voltage amplitude instruction;

[0011] Control the grid-forming converter low voltage ride through through the modified angular frequency instruction and the second modified voltage amplitude instruction;

[0012] After detecting the fault recovery instruction, the virtual impedance value and the power ring reference value are modified smoothly to control the grid-forming converter to smoothly exit the fault ride through state.

[0013] In some embodiments, the power ring reference value includes a reactive power reference value and an active power reference value, and the virtual impedance value includes a virtual resistance given value and a virtual inductance given value.

[0014] In some embodiments, the step of obtaining the reactive current injection reference value and the active current injection reference value of the grid-forming converter specifically comprises:

[0015] acquiring a grid voltage and performing coordinate transformation to obtain a direct-axis voltage and a quadrature-axis voltage;

[0016] comparing a nominal voltage of the grid with the direct-axis voltage to obtain a grid voltage drop level;

[0017] performing reactive power compensation calculation according to the grid voltage drop level and a quadrature-axis current corresponding to the quadrature-axis voltage to obtain a reactive current injection reference value of the grid-connected converter;

[0018] acquiring a remaining capacity of the grid, and performing difference theoretical calculation on the remaining capacity and the reactive current injection reference value to obtain an active current injection reference value.

[0019] In some embodiments, the step of calculating the power ring reference value during low voltage ride through of the droop control power ring specifically comprises:

[0020] performing instantaneous power calculation according to the reactive current injection reference value and the active current injection reference value in combination with the direct-axis voltage and the quadrature-axis voltage to obtain reactive power reference value and active power reference value of the droop control power ring during low voltage ride through.

[0021] In some embodiments, the step of sampling an actual current of the grid, obtaining a virtual impedance value in combination with the reactive current injection reference value and the active current injection reference value, determining a voltage amplitude compensation amount after obtaining a voltage drop value corresponding to the virtual impedance value to obtain the voltage amplitude compensation amount specifically comprises:

[0022] sampling an actual current of the grid to obtain a current sampling value, and performing coordinate transformation on the current sampling value to obtain a direct-axis sampling current and a quadrature-axis sampling current;

[0023] performing proportional integral adjustment after difference comparison between the active current injection reference value and the direct-axis sampling current to obtain a virtual resistance given value;

[0024] performing proportional integral adjustment after difference comparison between the reactive current injection reference value and the quadrature-axis sampling current to obtain a virtual inductance given value;

[0025] obtaining a direct-axis voltage compensation amount according to the virtual resistance given value and the direct-axis sampling current, and obtaining a quadrature-axis voltage compensation amount according to the virtual inductance given value and the quadrature-axis sampling current, wherein the direct-axis voltage compensation amount and the quadrature-axis voltage compensation amount constitute the voltage amplitude compensation amount.

[0026] In some embodiments, after detecting the fault recovery instruction, the step of performing smooth correction on the virtual impedance value and the power ring reference value to control the grid-connected converter to smoothly exit the fault ride through state specifically comprises:

[0027] exponentially decaying the virtual impedance value to obtain a real-time exit value of the virtual impedance value;

[0028] sampling and holding an active power output value at a moment when a fault recovery instruction is detected, and performing a smooth exponential increasing calculation with the active power reference value in the bypass normal operation state as a calculation end point to obtain a real-time exit value of the active power reference value;

[0029] sampling and holding a reactive power output value at a moment when a fault recovery instruction is detected, and performing a smooth exponential decaying calculation with the reactive power reference value in the bypass normal operation state as a calculation end point to obtain a real-time exit value of the reactive power reference value;

[0030] controlling the grid-forming converter to smoothly exit the fault ride-through state according to the real-time exit value of the virtual impedance value, the real-time exit value of the active power reference value, and the real-time exit value of the reactive power reference value.

[0031] In a second aspect, a low-voltage ride-through and recovery system of a grid-forming converter includes:

[0032] a droop control power loop correction module configured to obtain a reactive current injection reference value and an active current injection reference value of the grid-forming converter, and calculate a power loop reference value of the droop control power loop low-voltage ride-through according to the reactive current injection reference value and the active current injection reference value, and correct an angular frequency instruction and a voltage amplitude instruction of the grid-forming converter according to the power loop reference value to obtain a corrected angular frequency instruction and a first corrected voltage amplitude instruction;

[0033] a compensation amount determination module configured to sample an actual current of the power grid, and obtain a virtual impedance value in combination with the reactive current injection reference value and the active current injection reference value, and obtain a voltage amplitude compensation amount after determining a voltage drop value corresponding to the virtual impedance value;

[0034] a second correction module configured to correct the first corrected voltage amplitude instruction according to the voltage amplitude compensation amount to obtain a second corrected voltage amplitude instruction;

[0035] a ride-through control module configured to control the grid-forming converter to ride through a low voltage through the corrected angular frequency instruction and the second corrected voltage amplitude instruction;

[0036] a fault recovery module configured to, after detecting a fault recovery instruction, perform a smooth correction on the virtual impedance value and the power loop reference value to control the grid-forming converter to smoothly exit a fault ride-through state.

[0037] In a third aspect, a computer device comprises a memory, a processor, and a computer program stored in the memory and executable in the processor, and the processor implements the steps of the low-voltage ride-through and recovery method of the grid-forming converter when executing the computer program.

[0038] In a fourth aspect, a computer-readable storage medium stores a computer program, and the computer program implements the steps of the low-voltage ride-through and recovery method of the grid-forming converter when executed by a processor.

[0039] In a fifth aspect, a computer program product comprises a computer program, and the computer program implements the steps of the low-voltage ride-through and recovery method of the grid-forming converter when executed by a processor.

[0040] Compared with the prior art, the present application has the following beneficial effects:

[0041] The low-voltage ride-through and recovery method of the grid-forming converter provided by the present application controls the grid-forming converter to ride through low voltage by using the corrected angular frequency instruction and the twice corrected voltage amplitude instruction, and controls the grid-forming converter to smoothly exit the fault ride-through state by smoothing the virtual impedance value and the power loop reference value after detecting the fault recovery instruction, so as to avoid the impact current caused by the grid-forming converter under the conditions of grid voltage drop and fault recovery, and solve the problem of reactive power support demand.

[0042] Further, in the case where the grid-forming converter enters the droop control state to start low-voltage ride-through, the present application assumes that there is a virtual impedance between the low-voltage control point where the grid-forming converter is located and the AC bus, and determines the reactive current injection reference value and the active current injection reference value of the grid-forming converter according to the grid voltage drop level and the remaining capacity; obtains the virtual impedance value according to the reactive current injection reference value and the active current injection reference value to obtain the voltage amplitude compensation amount, so as to correct the voltage amplitude instruction and control the grid-forming converter to ride through low voltage in cooperation with the angular frequency instruction; and after detecting the fault recovery instruction, the power reference value, the active power reference value, and the virtual impedance value are smoothed to control the grid-forming converter to smoothly exit the fault ride-through state, so that the grid-forming converter provides reactive power support to the grid while ensuring a certain degree of active output during the low-voltage process, thereby avoiding the technical problems of impact current and reactive power support demand caused by the grid-forming converter under the conditions of grid voltage drop and fault recovery, and improving the reliability of low-voltage ride-through of the grid-forming converter.

[0043] Furthermore, this invention achieves precise compensation for voltage amplitude by dynamically adjusting the virtual impedance value through real-time sampling of the grid current and combining reactive current injection reference values ​​with active current injection reference values. This helps the converter maintain stable output during grid faults and avoids equipment damage caused by current surges or rapid reactive current injection. Attached Figure Description

[0044] Figure 1 A schematic flowchart illustrating the low-voltage ride-through and recovery method for a grid-type converter provided in an embodiment of the present invention;

[0045] Figure 2 This is a partial circuit diagram of a microgrid system according to an embodiment of the present invention;

[0046] Figure 3 This is the main circuit topology diagram of the low voltage ride-through and fault recovery control strategy provided in the embodiments of the present invention;

[0047] Figure 4 An equivalent circuit diagram for introducing virtual impedance provided in an embodiment of the present invention;

[0048] Figure 5 This is a block diagram of a voltage and current dual closed-loop control system with virtual impedance provided in an embodiment of the present invention.

[0049] Figure 6 This is a structural diagram of the low-voltage ride-through and recovery system of a grid-type converter provided in an embodiment of the present invention;

[0050] Figure 7 This is a schematic diagram of the computer equipment structure involved in the low voltage ride-through and recovery method of the grid-type converter in an embodiment of the present invention. Detailed Implementation

[0051] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. The content described herein is for explanation rather than limitation of the present invention.

[0052] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification and claims of this invention are intended to cover a non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, systems, products, or devices.

[0053] like Figure 1 As shown, this embodiment provides a low-voltage ride-through and recovery method for a grid-type converter, including the following steps:

[0054] S100, when the grid-type converter in the microgrid system enters the droop control state, calculate the reactive current injection reference value based on the real-time monitored grid voltage drop level;

[0055] In the event of a voltage drop in the power grid, at this time, such as Figure 3 As shown, the grid connection point voltage corresponding to the grid-connected converter. u pcc With nominal bus voltage u gN A voltage difference will occur between them. If the grid voltage drop level is defined... k The voltage drop level of the power grid k The calculation process is as follows: Formula (1):

[0056] (1)

[0057] In order to provide reactive power support to the power grid, the grid-type converter needs to inject reactive current into the power grid. The calculation process of the reference value of reactive current injection for low voltage ride-through is as follows: (2)

[0058] (2)

[0059] in, A reference value is injected for reactive current during low-voltage ride-through. This is the nominal current for normal operation.

[0060] S200, the active current injection reference value is calculated based on the remaining capacity and the reactive current injection reference value, specifically by the following formula (3):

[0061] (3)

[0062] in, A reference value is injected for the active current during low-voltage ride-through. .

[0063] S300, based on the reactive current injection reference value and the active current injection reference value, calculate the reactive power reference value and the active power reference value during the low voltage ride-through of the droop control power loop, and calculate by the following formula (4).

[0064] (4)

[0065] in, This is the voltage at the grid connection point.

[0066] S400, using reactive power reference values ​​and active power reference values, corrects the angular frequency command and voltage amplitude command of the grid-type converter during low voltage ride-through, obtaining the corrected angular frequency command and the first-corrected voltage amplitude command, calculated by the following formula (5):

[0067] (5)

[0068] wherein, is a corrected angular frequency instruction, is a first corrected voltage amplitude instruction, is a rated angular frequency of the grid-forming converter, is a rated voltage amplitude of the grid-forming converter, is an active droop coefficient, P is an actual active power output by the grid-forming converter, is an active power reference value for low voltage ride through of the grid-forming converter, is a reactive droop coefficient, Q is an actual reactive power output by the grid-forming converter, is a reactive power reference value for low voltage ride through of the grid-forming converter.

[0069] S500, sampling the actual current of the power grid to obtain a current sample value, and combining the reactive current injection reference value and the active current injection reference value to obtain a virtual resistance given value and a virtual inductance given value, and obtaining a voltage amplitude compensation amount;

[0070] Specifically, step S500 includes:

[0071] S510, sampling the actual current of the power grid to obtain a current sample value, and performing coordinate transformation on the current sample value to obtain a direct-axis sample current and a quadrature-axis sample current;

[0072] It should be noted that in S510, the coordinate transformation can include a Park transformation, and the coordinate transformation obtains a direct-axis current and a quadrature-axis current. Specifically, the angular frequency compensation amount can be determined according to the direct-axis current, and the voltage amplitude compensation amount can be determined according to the quadrature-axis current.

[0073] S520, after the active current injection reference value and the direct-axis sample current are compared and compared, proportional integral adjustment is performed to obtain a virtual resistance given value, which is calculated by the following formula (6):

[0074] (6)

[0075] After the reactive current injection reference value and the quadrature-axis sample current are compared and compared, proportional integral adjustment is performed to obtain a virtual inductance given value, which is calculated by the following formula (7):

[0076] (7)

[0077] In the above formulas (6) and (7), is a virtual resistance given value, a virtual inductance is given a value, an integral coefficient, an integral coefficient, a direct-axis sampling current, a quadrature-axis sampling current.

[0078] S530, according to the virtual resistance given value and the direct-axis sampling current, a direct-axis voltage compensation quantity is obtained, according to the virtual inductance given value and the quadrature-axis sampling current, a quadrature-axis voltage compensation quantity is obtained, the direct-axis voltage compensation quantity and the quadrature-axis voltage compensation quantity constitute the voltage amplitude compensation quantity, which is specifically realized by the following formula:

[0079] (8)

[0080] wherein, a direct-axis voltage compensation quantity, a quadrature-axis voltage compensation quantity;

[0081] As Figure 4 shown, after introducing the virtual impedance, the voltage drop generated on the virtual impedance can be obtained through the calculation of Kirchhoff's law in the two-phase rotating coordinate system, so as to obtain the voltage amplitude compensation quantity of low voltage ride through.

[0082] S600, according to the voltage amplitude compensation quantity under low voltage ride through, the voltage amplitude instruction after first correction is corrected to obtain the voltage amplitude instruction after second correction, which is calculated by the following formula (9):

[0083] (9)

[0084] wherein, a voltage loop direct-axis reference voltage, a voltage loop quadrature-axis reference voltage, a reactive droop power loop output voltage amplitude reference value instruction.

[0085] S700, the grid-connected converter low voltage ride through is controlled through the corrected angular frequency instruction and the voltage amplitude instruction after second correction, as Figure 5 shown, in the droop control state, the output voltage and frequency of the grid-connected converter in the droop control curve are respectively set as the voltage amplitude instruction after second correction and the angular frequency instruction after correction, the droop control curve is adjusted, and the grid-connected converter is controlled to control the grid-connected converter low voltage ride through.

[0086] S800, after detecting the fault recovery instruction, the virtual impedance value and the power loop reference value are smoothly corrected to control the grid-connected converter to smoothly exit the fault ride through state;

[0087] S800 includes:

[0088] S810, exponentially decaying calculation is performed on the virtual impedance value according to the following formula (10) to obtain a virtual impedance real-time exit value;

[0089] (10)

[0090] In formula (9) is a virtual resistance real-time exit value in the fault recovery process, is a virtual inductance real-time exit value in the fault recovery process, is a decay coefficient.

[0091] S820, according to the following formula (11), the active power output value at the moment when the fault recovery instruction is detected is sampled and held, and the active power reference value in the bypass normal operation state is taken as a calculation end point to perform a smooth exponential increase calculation to obtain a real-time exit value of the active power reference value;

[0092] (11)

[0093] wherein, is a real-time exit value of the active power reference value in the fault recovery process, is a sampled active power output value at the moment when the fault recovery instruction is detected, is an active power reference value in the bypass normal operation state, is a decay coefficient.

[0094] S830, according to the following formula (12), the reactive power output value at the moment when the fault recovery instruction is detected is sampled and held, and the reactive power reference value in the bypass normal operation state is taken as a calculation end point to perform a smooth exponential decay calculation to obtain a real-time exit value of the reactive power reference value;

[0095] (12)

[0096] wherein, is a real-time exit value of the reactive power reference value in the fault recovery process, is a sampled active power output value at the moment when the fault recovery instruction is detected, is an active power reference value in the bypass normal operation state, is a decay coefficient.

[0097] The low-voltage ride-through and recovery method of the grid-forming converter provided in the embodiment above, in the case that the grid-forming converter enters the droop control state to start low-voltage ride-through, assumes that there is a virtual impedance between the low-voltage control point where the grid-forming converter is located and the AC bus, and determines the reactive current injection reference value and the active current injection reference value of the low-voltage ride-through according to the grid voltage drop level, to obtain the reactive power reference value and the active power reference value of the low-voltage ride-through, corrects the angular frequency instruction and the voltage amplitude instruction of the grid-forming converter in the low-voltage ride-through through the power loop reference value of the droop control power loop in the low-voltage ride-through, obtains the voltage amplitude compensation amount through the virtual impedance value obtained by the reactive current reference value and the active current reference value of the low-voltage ride-through, and corrects the voltage amplitude instruction of the low-voltage ride-through again to control the low-voltage ride-through of the grid-forming converter. After the fault recovery instruction is detected, the virtual impedance value and the power loop reference value are smoothed and corrected to control the grid-forming converter to smoothly exit the fault ride-through state, so as to realize the correction of the control instruction of the grid-forming converter in the case of grid voltage drop, so that the grid-forming converter can provide reactive power support to the grid in the low-voltage process while ensuring a certain degree of active output, thereby avoiding the technical problems of impact current and reactive power support demand of the grid-forming converter in the case of grid voltage drop and fault recovery, and improving the reliability of the low-voltage ride-through of the grid-forming converter. The method can be applied to smooth low-voltage ride-through and recovery in the case of grid symmetrical fault.

[0098] As shown in Figure 6 The embodiment further provides a low-voltage ride-through and recovery system of a grid-forming converter, which comprises:

[0099] A droop control power loop correction module is configured to obtain the reactive current injection reference value and the active current injection reference value of the grid-forming converter, calculate the power loop reference value of the droop control power loop in the low-voltage ride-through according to the reactive current injection reference value and the active current injection reference value, correct the angular frequency instruction and the voltage amplitude instruction of the grid-forming converter according to the power loop reference value, and obtain the corrected angular frequency instruction and the first corrected voltage amplitude instruction.

[0100] A compensation amount determination module is configured to sample the actual current of the grid, obtain the virtual impedance value in combination with the reactive current injection reference value and the active current injection reference value, obtain the voltage amplitude compensation amount after determining the voltage drop value corresponding to the virtual impedance value, and correct the first corrected voltage amplitude instruction according to the voltage amplitude compensation amount to obtain the second corrected voltage amplitude instruction.

[0101] A secondary correction module is configured to correct the first corrected voltage amplitude instruction according to the voltage amplitude compensation amount to obtain the second corrected voltage amplitude instruction.

[0102] A ride-through control module is configured to control the low-voltage ride-through of the grid-forming converter through the corrected angular frequency instruction and the second corrected voltage amplitude instruction.

[0103] The fault recovery module is configured to, after detecting the fault recovery instruction, perform smooth correction on the virtual impedance value and the power loop reference value, and control the grid-forming converter to smoothly exit the fault ride-through state.

[0104] The division of the modules in the embodiments of the present application is illustrative, and is merely a logical functional division. In actual implementation, another division manner can be used. In addition, each functional module in each embodiment of the present application can be integrated in one processor, or can be physically separated, or two or more modules can be integrated in one module. The integrated module can be implemented in the form of hardware or in the form of a software functional module.

[0105] The embodiment further provides a computer device including a processor and a memory. The memory is used to store a computer program (the computer program includes a calculation component and an iteration component, and can perform model calculation and model updating). The computer program includes program instructions. The processor is used to execute the program instructions stored in the computer storage medium. The processor can be a central processing unit (CPU), and can also be another general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or another programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, and the like. The processor is a computing core and a control core of the terminal, and is suitable for implementing one or more instructions. Specifically, the processor is suitable for loading and executing one or more instructions in the computer storage medium to implement a corresponding method flow or a corresponding function. The processor in the embodiment of the present application can be used for the operation of the low-voltage ride-through and recovery method of the grid-forming converter.

[0106] Reference is made below to Figure 7 which shows a structural schematic diagram of a low-voltage ride-through and fault recovery control device suitable for being used to implement the embodiments of the present application. The low-voltage ride-through and fault recovery control device in the embodiments of the present application can include, but is not limited to, a mobile terminal such as a notebook computer, a PDA (Personal Digital Assistant: personal digital assistant), a PAD (Portable Application Description: tablet computer), and the like, and a fixed terminal such as a desktop computer and the like. Figure 7The low voltage ride through and fault recovery control device shown is merely an example and should not impose any limitation on the function and use range of the embodiments of the present application.

[0107] As shown in Figure 7 The computer device can include a processing device 1001 (e.g., a central processing unit, a graphics processing unit, etc.) that can perform various appropriate actions and processes according to a program stored in a read only memory (ROM) 1002 or a program loaded from a storage device 1003 into a random access memory (RAM) 1004. Various programs and data required for operation of the computer device are also stored in the RAM 1004. The processing device 1001, the ROM 1002, and the RAM 1004 are connected to each other through a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Generally, the following systems can be connected to the I / O interface 1006: input devices 1007 including, for example, a touch screen, a touch pad, a keyboard, a mouse, an image sensor, a microphone, etc.; output devices 1008 including, for example, a liquid crystal display (LCD), a speaker, etc.; the storage device 1003 including, for example, a magnetic tape, a hard disk, etc.; and a communication device 1009. The communication device 1009 can allow the low voltage ride through and fault recovery control device to communicate with other devices wirelessly or by wire to exchange data. The computer device can be the low voltage ride through and fault recovery control device.

[0108] In particular, according to the embodiments disclosed in the present application, the processes described above with reference to the flowcharts can be implemented as a computer software program. The embodiments disclosed in the present application include a computer program product comprising a computer program carried on a computer readable medium, the computer program containing program codes for executing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network through the communication device, or installed from the storage device 1003, or installed from the ROM 1002. When the computer program is executed by the processing device 1001, the above-mentioned functions defined in the methods of the embodiments disclosed in the present application are performed.

[0109] The computer device provided in the present application adopts the low voltage ride through and recovery method of the network-forming converter in the above-mentioned embodiments, and can solve the technical problems of impact current and reactive power support demand of the network-forming converter under the conditions of grid voltage drop and fault recovery.

[0110] The embodiment further provides a storage medium, specifically, a computer readable storage medium (Memory). The computer readable storage medium is a memory device in a computer device, and is used to store programs and data. It can be understood that the computer readable storage medium herein can include an internal storage medium in the computer device, and of course can include an extended storage medium supported by the computer device. The computer readable storage medium provides a storage space, and the storage space stores an operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and the instructions can be one or more computer programs (including program codes). It should be noted that the computer readable storage medium herein can be a high-speed RAM memory, or a non-volatile memory such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer readable storage medium to implement the corresponding steps of the low-voltage ride-through and recovery method of the network-forming converter in the above embodiment.

[0111] The embodiment further provides a computer program product, which includes a computer program. When the computer program is executed by the processor, the corresponding steps of the low-voltage ride-through and recovery method of the network-forming converter in the above embodiment are implemented.

[0112] 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 an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. In addition, 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.) containing computer usable program code.

[0113] The present application is described with reference to flowcharts and / or block diagrams of the method, device (system), and computer program product according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one or more flows and / or blocks Figure 1 The device that implements the functions specified in one or more flows and / or blocks.

[0114] These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the flow Figure 1 The functions of a flow or multiple flows and / or a block or multiple blocks in conjunction with the disclosed methods. Figure 1

[0115] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flow Figure 1 The functions of a flow or multiple flows and / or a block or multiple blocks in conjunction with the disclosed methods. Figure 1 The functions of a flow or multiple flows and / or a block or multiple blocks in conjunction with the disclosed methods.

[0116] Finally, it should be noted that the above-mentioned embodiments are merely used to illustrate the technical solutions of the present application, rather than limiting the same. Even though the present application has been described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced equivalently, and any modification or replacement without departing from the spirit and scope of the present application should be covered within the protection scope of the claims of the present application.​

Claims

1. A method for low voltage ride through and recovery of a meshed network converter, characterized in that, The method comprises the following steps: obtaining a reactive current injection reference value and an active current injection reference value of the grid-connected converter, and calculating a power loop reference value of the power loop low voltage ride through according to the reactive current injection reference value and the active current injection reference value, correcting an angular frequency instruction and a voltage amplitude instruction of the grid-connected converter according to the power loop reference value, and obtaining a corrected angular frequency instruction and a first corrected voltage amplitude instruction; sampling an actual current of the power grid, obtaining a virtual impedance value in combination with the reactive current injection reference value and the active current injection reference value, obtaining a voltage amplitude compensation amount after determining a voltage drop value corresponding to the virtual impedance value; correcting the first corrected voltage amplitude instruction according to the voltage amplitude compensation amount, and obtaining a second corrected voltage amplitude instruction; controlling the grid-connected converter low voltage ride through through the corrected angular frequency instruction and the second corrected voltage amplitude instruction; after detecting a fault recovery instruction, performing smooth correction on the virtual impedance value and the power loop reference value, and controlling the grid-connected converter to smoothly exit the fault ride through state; the power loop reference value comprises a reactive power reference value and an active power reference value, and the virtual impedance value comprises a virtual resistance given value and a virtual inductance given value; the step of sampling the actual current of the power grid, obtaining the virtual impedance value in combination with the reactive current injection reference value and the active current injection reference value, and obtaining the voltage amplitude compensation amount after determining the voltage drop value corresponding to the virtual impedance value specifically comprises: sampling the actual current of the power grid to obtain a current sampling value, and performing coordinate transformation on the current sampling value to obtain a direct axis sampling current and a quadrature axis sampling current; after comparing the active current injection reference value and the direct axis sampling current, performing proportional integral adjustment to obtain the virtual resistance given value; after comparing the reactive current injection reference value and the quadrature axis sampling current, performing proportional integral adjustment to obtain the virtual inductance given value; obtaining a direct axis voltage compensation amount according to the virtual resistance given value and the direct axis sampling current, and obtaining a quadrature axis voltage compensation amount according to the virtual inductance given value, wherein the direct axis voltage compensation amount and the quadrature axis voltage compensation amount constitute the voltage amplitude compensation amount; after detecting the fault recovery instruction, the step of performing smooth correction on the virtual impedance value and the power loop reference value, and controlling the grid-connected converter to smoothly exit the fault ride through state specifically comprises: performing exponential decay calculation on the virtual impedance value to obtain a virtual impedance real-time exit value; sampling and holding an active power output value at the moment when the fault recovery instruction is detected, and performing smooth exponential increase calculation with the active power reference value in the bypass normal running state as a calculation terminal point to obtain an active power reference value real-time exit value; sampling and holding a reactive power output value at the moment when the fault recovery instruction is detected, and performing smooth exponential decay calculation with the reactive power reference value in the bypass normal running state as a calculation terminal point to obtain a reactive power reference value real-time exit value; controlling the grid-connected converter to smoothly exit the fault ride through state according to the virtual impedance real-time exit value, the active power reference value real-time exit value, and the reactive power reference value real-time exit value.

2. The method of claim 1, wherein, The power ring reference value comprises a reactive power reference value and an active power reference value, and the virtual impedance value comprises a virtual resistance given value and a virtual inductance given value.

3. The method of claim 2, wherein, The step of obtaining the reactive current injection reference value and the active current injection reference value of the grid-connected converter comprises: obtaining grid voltage and performing coordinate transformation to obtain direct-axis voltage and quadrature-axis voltage; comparing the nominal voltage of the grid with the direct-axis voltage to obtain the grid voltage drop level; performing reactive power compensation calculation according to the grid voltage drop level and the quadrature-axis current corresponding to the quadrature-axis voltage to obtain the reactive current injection reference value of the grid-connected converter; obtaining the remaining capacity of the grid and performing difference theoretical calculation on the remaining capacity and the reactive current injection reference value to obtain the active current injection reference value.

4. The method of claim 3, wherein, The step of calculating the power ring reference value during low voltage ride-through of the droop control power ring comprises: performing instantaneous power calculation according to the reactive current injection reference value and the active current injection reference value in combination with the direct-axis voltage and the quadrature-axis voltage to obtain the reactive power reference value and the active power reference value of the droop control power ring during low voltage ride-through.

5. A low voltage ride through and restoration system for a meshed converter, characterized in that, The low voltage ride-through and recovery method of the grid-connected converter according to any one of claims 1-4 comprises: a droop control power ring correction module configured to obtain the reactive current injection reference value and the active current injection reference value of the grid-connected converter, and calculate the power ring reference value during low voltage ride-through of the droop control power ring according to the reactive current injection reference value and the active current injection reference value, and correct the angular frequency instruction and the voltage amplitude instruction of the grid-connected converter according to the power ring reference value to obtain the corrected angular frequency instruction and the first corrected voltage amplitude instruction; a compensation amount determination module configured to sample the actual current of the grid, and obtain a virtual impedance value in combination with the reactive current injection reference value and the active current injection reference value, and obtain a voltage amplitude compensation amount after determining the voltage drop value corresponding to the virtual impedance value; a second correction module configured to correct the first corrected voltage amplitude instruction according to the voltage amplitude compensation amount to obtain a second corrected voltage amplitude instruction; a ride-through control module configured to control the grid-connected converter to ride through low voltage through the corrected angular frequency instruction and the second corrected voltage amplitude instruction; a fault recovery module configured to perform smooth correction on the virtual impedance value and the power ring reference value after detecting a fault recovery instruction to control the grid-connected converter to smoothly exit the fault ride-through state.

6. A computer device, comprising: The computer readable storage medium stores a computer program, and the computer program is executed by the processor to implement the steps of the low voltage ride-through and recovery method of the grid-connected converter according to any one of claims 1-4.

7. A computer-readable storage medium, characterized in that, The computer program is executed by the processor to implement the steps of the low voltage ride-through and recovery method of the grid-connected converter according to any one of claims 1-4.

8. A computer program product comprising a computer program, characterized in that, The computer program is executed by the processor to implement the steps of the low voltage ride-through and recovery method of the grid-connected converter according to any one of claims 1-4.

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