Network construction control method and device for voltage source type power electronic equipment

Abstract

The embodiment of the invention relates to the technical field of power electronic control, and provides a network construction control method and device for voltage source type power electronic equipment, and the method comprises the steps: judging a fault level when a fault occurs in a target power grid; determining a starting judgment strategy of virtual impedance based on the fault level; the virtual impedance is started based on the starting judgment strategy, network construction control current limiting is carried out by adopting the virtual impedance under a three-phase static coordinate system, and the three-phase static coordinate system is the basis for limiting the equipment current in the target power grid within the overcurrent capacity through network construction control; and controlling the voltage source type power electronic equipment to perform network construction control on the target power grid in the network construction control current limiting state. Therefore, the over-current problem caused by an alternating-current fault can be well solved, and the operation reliability of actual equipment is improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronic control technology, and in particular, to a grid-forming control method and device for a voltage-source power electronic device. Background Art

[0002] As the proportion of new energy in the AC system is getting higher and higher, the control characteristics of power electronic devices pose challenges to the stable operation control of traditional power systems. With the in-depth study of the stability of high-proportion new energy AC systems, higher requirements are also put forward for the control characteristics of power electronic devices. Grid-Forming Control is a new power system control technology. In order to better meet the stability requirements of traditional power systems, this control technology is gradually applied to power electronic devices such as new energy power generation (such as wind energy, photovoltaic), energy storage, and new energy transmission systems. The grid-forming control technology mainly simulates the characteristics of traditional synchronous generators to provide voltage and frequency support. Grid-forming control needs to consider that under the condition of limited overcurrent capacity of actual equipment, the safe and stable operation of grid-forming control faces challenges.

[0003] In the case of power system faults, due to the limitation of equipment overcurrent capacity, grid-forming control needs to dynamically adjust the output current to limit the current within a safe range to avoid equipment damage. The literature "Modeling and Improved Control of Virtual Synchronous Generators under Grid Symmetrical Faults" adopts virtual resistance technology and phasor current limiting technology, which can limit the fault current of virtual synchronous generators during grid faults and ensure their safe operation without tripping during grid faults. This literature considers current limiting under grid symmetrical faults, and the phasor current limiting technology is implemented in the rotating coordinate system, which requires time to extract sequence components and is slower in control compared to the stationary coordinate system. Summary of the Invention

[0004] The present invention provides a grid-forming control method and device for a voltage-source power electronic device, aiming to solve the defect that the grid-forming control current limiting function is imperfect due to the limitation of equipment overcurrent capacity in different power system fault conditions in the prior art, and to realize that the grid-forming control can well cope with the overcurrent problem caused by AC faults and improve the operation reliability of actual equipment.

[0005] The present invention provides a grid-forming control method for a voltage-source power electronic device, including: When a target power grid fails, judge the fault level; Determine the starting judgment strategy of the virtual impedance based on the fault level; Start the virtual impedance based on the starting judgment strategy, and use the virtual impedance for grid-forming control current limiting in the three-phase stationary coordinate system, where the three-phase stationary coordinate system is the basis for the grid-forming control to limit the equipment current in the target power grid within the overcurrent capacity. Under the grid-forming control current-limiting state, control the voltage-source power electronic device to perform grid-forming control on the target power grid, and generate three-phase virtual voltages according to the virtual impedance to achieve the purpose of current limiting.

[0006] In a possible implementation manner, the method further includes: Detect the instantaneous values of the three-phase alternating current of the target power grid and the modulus value of the positive-sequence component of the three-phase alternating voltage; If the instantaneous value of the current is greater than or equal to the preset equipment over-current setting value or the modulus value of the positive-sequence component of the voltage is less than the first-level fault positive-sequence voltage setting value, determine that the fault level is a first-level fault; Detect the effective values of the three-phase alternating voltages of the target power grid; If the modulus value of the positive-sequence component of the voltage or the effective value of the voltage is between the lower limit of normal operation of the target power grid and the preset positive-sequence voltage or the effective value of the voltage, determine that the fault level is a second-level fault.

[0007] In a possible implementation manner, the method further includes: If it is determined that the fault level is a first-level fault, immediately start the virtual impedance, and the start judgment strategy is to start the virtual impedance through the instantaneous value of the current or the voltage criterion; If it is determined that the fault level is a second-level fault, the start judgment strategy is to start the virtual impedance through the voltage criterion.

[0008] In a possible implementation manner, the method further includes: After starting the virtual impedance, superimpose a virtual voltage drop on the potential voltage in the three-phase stationary coordinate system of the target power grid, and limit the current passing through the equipment in the target power grid through the virtual voltage drop corresponding to the virtual impedance.

[0009] In a possible implementation manner, the method further includes: Calculate the voltage drop generated by the virtual impedance; Determine the corresponding virtual voltage drop based on the voltage drop generated by the virtual impedance, and generate a target modulation wave based on the virtual voltage drop; Control the switching actions of the voltage-source power electronic device based on the target modulation wave, and control the output current and voltage; Limit the current passing through the equipment in the target power grid through the voltage output by the voltage-source power electronic device.

[0010] In a possible implementation manner, the method further includes: During the process of controlling the voltage-source power electronic device to perform grid-forming control on the target power grid, continuously monitor the changes in current and voltage; Dynamically adjust the virtual impedance based on the changes in the current and voltage.

[0011] In a possible implementation, the method further includes: Determine the value of the virtual impedance based on the overcurrent capacity of the voltage source type power electronic device.

[0012] The present invention also provides a grid-forming control device for a voltage source type power electronic device, including the following modules: A judgment module, configured to judge the fault level when a target power grid fails; A determination module, configured to determine a startup judgment strategy for the virtual impedance based on the fault level; A control module, configured to start the virtual impedance based on the startup judgment strategy, and perform grid-forming control to limit current by using the virtual impedance in a three-phase static coordinate system, where the three-phase static coordinate system is the basis for quickly limiting the device current in the target power grid within the overcurrent capacity during grid-forming control; The control module is further configured to, in the state of grid-forming control for current limiting, control the voltage source type power electronic device to perform grid-forming control on the target power grid, and generate three-phase virtual voltages according to the virtual impedance so as to achieve the purpose of current limiting.

[0013] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the grid-forming control method of the voltage source type power electronic device as described in any one of the above is implemented.

[0014] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the grid-forming control method of the voltage source type power electronic device as described in any one of the above is implemented.

[0015] The present invention also provides a computer program product, including a computer program. When the computer program is executed by a processor, the grid-forming control method of the voltage source type power electronic device as described in any one of the above is implemented.

[0016] The network-forming control method and device for a voltage-source power electronic device provided by the present invention determine the fault level when a target power grid fails; determine the investment strategy of the virtual impedance based on the fault level; start the virtual impedance based on the investment strategy, and perform network-forming control current limiting using the virtual impedance in the three-phase static coordinate system, where the three-phase static coordinate system is the basis for network-forming control to limit the device current in the target power grid within the overcurrent capacity; in the state of network-forming control current limiting, control the voltage-source power electronic device to perform network-forming control on the target power grid, and generate three-phase virtual voltages according to the virtual impedance to achieve the purpose of current limiting. Compared with the defect in the prior art that the network-forming control current limiting function is imperfect due to the limitation of the overcurrent capacity of the device in different fault situations of the power system, in this solution, current limiting of the virtual impedance is realized in the three-phase static coordinate system. For devices with limited overcurrent capacity, the current limiting measures realized in this coordinate system do not require a filtering link. When a first-level fault occurs, the virtual impedance is started using the instantaneous value of the current or the voltage criterion, so that the current limiting function can be realized more quickly; at the same time, the stable operation in the case of a second-level fault is also considered, and the virtual impedance start criterion is added using the modulus value or the effective value of the positive-sequence voltage component to avoid repeated switching of the virtual impedance, and the current is limited within the overcurrent capacity of the device, which can well handle the overcurrent problem caused by AC faults and improve the operation reliability of the actual device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 is one of the flow charts of the network-forming control method for a voltage-source power electronic device provided by the present invention.

[0019] Figure 2 is the second flow chart of the network-forming control method for a voltage-source power electronic device provided by the present invention.

[0020] Figure 3 is the structural diagram of the network-forming control method for a voltage-source power electronic device provided by the present invention.

[0021] Figure 4 is the structural diagram of the network-forming control device for a voltage-source power electronic device provided by the present invention.

[0022] Figure 5 is the structural diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0024] To facilitate the understanding of the embodiments of the present invention, the following will further explain with specific embodiments in conjunction with the accompanying drawings. The embodiments do not constitute a limitation to the embodiments of the present invention.

[0025] Figure 1 is one of the schematic flowcharts of the grid-forming control method for a voltage-source power electronic device provided by the present invention. As Figure 1 shown, the method includes the following: S11. When a fault occurs in the target power grid, judge the fault level.

[0026] The current-limiting method based on virtual impedance in the embodiments of the present invention is implemented in the three-phase stationary coordinate system. For devices with limited overcurrent capacity, the current-limiting measures implemented in this coordinate system do not require a filtering link. This measure is the basis for quickly implementing current limiting. During a severe fault, the virtual impedance is started using the instantaneous value of the current or voltage criterion, so that the current-limiting function can be realized more quickly; at the same time, the stable operation during a minor fault is also considered, and the virtual impedance criterion is started by adding the modulus value or effective value of the positive-sequence voltage component, avoiding repeated switching on and off of the virtual impedance; due to the use of the three-phase stationary coordinate system, the virtual impedance can limit the current within the overcurrent capacity of the device for both symmetrical and asymmetrical fault conditions.

[0027] Specifically, when a fault occurs in the target power grid, detect the instantaneous value of the three-phase alternating current and the modulus value of the positive-sequence voltage component of the three-phase alternating voltage of the target power grid. If the instantaneous value of the current is greater than or equal to the preset overcurrent setting value of the device or the modulus value of the positive-sequence voltage component is less than the positive-sequence voltage setting value of the first-level fault, determine that the fault level is a first-level fault (severe fault). Detect the effective value of the three-phase alternating voltage of the target power grid. If the modulus value of the positive-sequence voltage component or the effective value of the voltage is between the lower limit value of the normal operation of the target power grid and the preset positive-sequence voltage or voltage effective value setting value, determine that the fault level is a second-level fault (minor fault).

[0028] S12. Determine the starting judgment strategy of the virtual impedance based on the fault level.

[0029] S13. Start the virtual impedance based on the starting judgment strategy, and use the virtual impedance for grid-forming control current limiting in the three-phase stationary coordinate system.

[0030] The voltage source type power electronic device can be a medium - low voltage two - level fully - controlled power electronic device or a medium - high voltage multi - level cascaded power electronic device. By adopting the current - free inner - loop network - forming control current - limiting method proposed in the present invention in the above - mentioned devices, especially under the condition that the over - current capacity of the device is limited, it can well cope with the over - current problem caused by AC faults, improve the operation reliability of the actual device and also have high economy.

[0031] In the three - phase static coordinate system, by superimposing the voltage drop generated by the virtual impedance on the modulation wave, the fast current - limiting function under the AC fault condition is realized. The three - phase static coordinate system is the basis for the network - forming control to quickly limit the current of the device in the target power grid within the over - current capacity.

[0032] If it is determined that the fault level is a first - level fault, the corresponding virtual impedance is adopted, that is, when the current exceeds the limit or the voltage amplitude is less than the threshold, the corresponding virtual impedance is put into use to quickly limit the current.

[0033] The value of the virtual impedance is determined by the actual hardware over - current capacity, ensuring that under different voltage sag degrees, the virtual impedance can still limit the current within the hardware over - current capacity.

[0034] If it is determined that the fault level is a second - level fault, the start - up judgment strategy is to start the virtual impedance through the voltage criterion to avoid the repeated switching - on and off of the virtual impedance. In this case, although the current may not have reached the over - current setting value, the drop in voltage already indicates that there may be potential problems in the system, and measures need to be taken to maintain stable operation.

[0035] S14. In the state of network - forming control current - limiting, control the voltage source type power electronic device to perform network - forming control on the target power grid.

[0036] Through the above - mentioned network - forming control current - limiting measures, the voltage source type power electronic device can quickly and effectively limit the current during power grid faults, and at the same time provide necessary voltage and frequency support for the power grid to ensure the stable operation of the target power grid.

[0037] The network-forming control method and device for a voltage-source power electronic device provided by the present invention determine the fault level when a target power grid fails; determine a starting judgment strategy for a virtual impedance based on the fault level; start the virtual impedance based on the starting judgment strategy, and perform network-forming control current limiting using the virtual impedance in a three-phase stationary coordinate system, where the three-phase stationary coordinate system is the basis for quickly limiting the device current in the target power grid within the overcurrent capacity during network-forming control; in the state of network-forming control current limiting, control the voltage-source power electronic device to perform network-forming control on the target power grid, and quickly generate three-phase virtual voltages based on the virtual impedance to achieve the purpose of current limiting. Compared with the defect in the prior art that the network-forming control current limiting function is imperfect due to the limitation of the device overcurrent capacity under different fault conditions in the power system, in this solution, current limiting of the virtual impedance is achieved in the three-phase stationary coordinate system. For devices with limited overcurrent capacity, the current limiting measures implemented in this coordinate system do not require a filtering link. In the event of a severe fault, the virtual impedance is started using the current instantaneous value or voltage criterion, so that the current limiting function can be achieved more quickly; at the same time, the stable operation during a minor fault is also considered, and the virtual impedance starting criterion is added with the modulus value or effective value of the positive-sequence voltage component to avoid repeated switching of the virtual impedance, and the current is limited within the overcurrent capacity of the device, which can well handle the overcurrent problem caused by AC faults and improve the reliability of the actual device operation.

[0038] Figure 2 It is the second schematic flow chart of the network-forming control method for the voltage-source power electronic device provided by the present invention. As Figure 2 shown, the method includes the following: The current limiting method based on the virtual impedance in the embodiment of the present invention is implemented in the three-phase stationary coordinate system. For devices with limited overcurrent capacity, the current limiting measures implemented in this coordinate system do not require a filtering link. In the event of a severe fault, the virtual impedance is started using the current instantaneous value or voltage criterion, so that the current limiting function can be achieved more quickly; at the same time, the stable operation during a minor fault is also considered, and the virtual impedance starting criterion is added with the modulus value or effective value of the positive-sequence voltage component to avoid repeated switching of the virtual impedance; since the present invention uses the three-phase stationary coordinate system, the virtual impedance can limit the current within the overcurrent capacity of the device for both symmetrical and asymmetrical fault conditions.

[0039] S21. Detect the current instantaneous values of the three-phase alternating current and the modulus value of the positive-sequence voltage component of the three-phase alternating voltage of the target power grid.

[0040] Specifically, when a fault occurs in the target power grid, the instantaneous values of the three-phase alternating current and the modulus value of the positive-sequence component of the three-phase alternating voltage in the target power grid are monitored in real time. The instantaneous value of the current refers to the actual value of the current at a specific moment. Since the alternating current is a sine wave that changes with time, by detecting the instantaneous value of the current, the state of the current at each moment can be accurately grasped, providing basic data for subsequent fault judgment; the modulus value of the positive-sequence component of the voltage is an important parameter considering factors such as the phase sequence of the voltage, which can reflect the symmetry and quality of the power grid voltage.

[0041] S22. If the instantaneous value of the current is greater than or equal to the preset over-current setting value of the device or the modulus value of the positive-sequence component of the voltage is less than the first-level fault positive-sequence voltage setting value, determine that the fault level is a first-level fault.

[0042] Compare the detected instantaneous value of the current with the preset over-current setting value of the device. The over-current setting value of the device is a threshold determined based on factors such as the rated current of the power grid device and the allowable maximum overload current. If the instantaneous value of the current is greater than or equal to this over-current setting value of the device, it means that the current in the power grid has exceeded the range that the device can safely withstand. At this time, determine that the fault level is a first-level fault. A first-level fault is a relatively serious type of fault, indicating that there may be serious problems such as a short circuit in the power grid and immediate measures need to be taken.

[0043] S23. Detect the effective values of the three-phase alternating voltage of the target power grid.

[0044] Detect the three-phase alternating voltage of the target power grid. The modulus value of the positive-sequence component of the voltage or the effective value of the voltage can be detected. The modulus value of the positive-sequence component of the voltage is an important parameter considering factors such as the phase sequence of the voltage, which can reflect the symmetry and quality of the power grid voltage; the effective value of the voltage is a commonly used index to measure the magnitude of the alternating voltage, which represents the average level of the alternating voltage in one cycle.

[0045] S24. If the modulus value of the positive-sequence component of the voltage or the effective value of the voltage is between the lower limit value of the normal operation of the target power grid and the preset positive-sequence voltage or the effective value of the voltage, determine that the fault level is a second-level fault.

[0046] Compare the detected modulus value of the positive-sequence component of the voltage or the effective value of the voltage with the lower limit value of the normal operation of the target power grid and the preset positive-sequence voltage setting value or the effective value of the voltage. The preset positive-sequence voltage setting value is a relatively low voltage threshold. When the voltage is lower than this value, it means that the power grid voltage has dropped severely, which may be caused by a power grid fault. If the modulus value of the positive-sequence component of the voltage is less than the preset positive-sequence voltage setting value, then determine that the fault level is a second-level fault.

[0047] The lower limit of the normal operation of the target power grid is the lowest voltage value allowed when the power grid is operating normally. When the voltage is within this range, although it does not reach the severity of a first-level fault, there are still certain abnormal conditions and it needs to be handled according to a second-level fault.

[0048] S25. If it is determined that the fault level is a first-level fault, the virtual impedance is immediately started, and the start judgment strategy is to start the virtual impedance through the instantaneous value of the current or the voltage criterion.

[0049] If it is determined through the previous judgment that the fault level is a first-level fault, direct measures need to be taken immediately to deal with it, so the virtual impedance is directly started. The virtual impedance is an impedance simulated through software algorithms and other means, and it can limit the current in the power grid.

[0050] S26. If it is determined that the fault level is a second-level fault, the start judgment strategy is to start the virtual impedance through the voltage criterion.

[0051] If it is determined that the fault level is a second-level fault, then the virtual impedance needs to be started through the voltage criterion. The voltage criterion is to judge whether the conditions for starting the virtual impedance are met based on relevant parameters of the voltage (such as the modulus value of the positive sequence component of the voltage or the effective value of the voltage, etc.). Because the second-level fault is less severe than the first-level fault, it is necessary to decide whether to start the virtual impedance according to the specific situation of the voltage to achieve more precise control.

[0052] After starting the virtual impedance, the virtual impedance is superimposed on the electromotive force voltage in the three-phase stationary coordinate system of the target power grid, and the current passing through the equipment in the target power grid is limited by the virtual voltage drop corresponding to the virtual impedance.

[0053] Combined with Figure 3 the structural schematic diagram of the grid-forming control method of the voltage-source power electronic device shown, where, and are respectively the actual value and the target value of the active power; is the frequency reference value; is the virtual moment of inertia; is the damping coefficient; 、 are the amplitude and phase angle of the internal electromotive force generated by the power outer loop; , , is the internal electromotive force generated by the power outer loop in the three-phase stationary coordinate system; , , is the actual AC current instantaneous value; is the time constant; , are the virtual resistance and the virtual inductance; , , is the voltage drop of the virtual impedance in the three-phase static coordinate system; , , is the final modulation wave in the three-phase static coordinate system. In the three-phase static coordinate system, the fast current limiting function under AC fault conditions is achieved by superimposing the voltage drop generated by the virtual impedance on the modulation wave. The calculation method of the virtual impedance is as follows: Hierarchical virtual impedance is adopted, that is, when the current exceeds the limit or the voltage amplitude is less than the threshold (primary fault) or the modulus of the positive sequence component of the voltage or the effective value of the voltage is between the lower limit of the normal operation of the grid voltage and the positive sequence voltage setting value of the primary fault (secondary fault), the virtual impedance calculated by the following formula is input:

[0054] [[ID=1S]]where is the instantaneous value of the actual current, is the overcurrent setting value (matched with the overcurrent capacity of the device), is the positive sequence voltage setting value for severe faults, is the angular frequency of the AC system, is the virtual resistance, is the virtual reactance, is the virtual inductance, is the value of the virtual resistance to be input, is the lower limit of the normal operation of the grid voltage.

[0055] Similarly, in order to ensure a better current limiting effect, considering the hardware overcurrent capacity and the degree of voltage drop, the constraint condition is

[0056] It can be solved that:

[0057]

[0058] where is the instantaneous value of the actual current, is the overcurrent capacity of the device, is the ratio of the reactance to the resistance of the virtual impedance, is the modulus or effective value of the positive sequence component of the actual voltage, is the actual equivalent resistance of the device, is the actual reactance of the device, is the rated voltage value of the bus to which the device is connected, is the voltage calculation threshold of the virtual impedance.

[0059] In summary, the specific value corresponding to the virtual impedance can be calculated, but the key issue to be considered is how to implement the virtual reactance in the three-phase stationary coordinate system.

[0060] The virtual reactance should originally be simulated by However, since the integral link s is unstable and very susceptible to interference, a first-order inertia link is considered to form a lead regulation link. Among them, is the corner frequency of the inertia link.

[0061]

[0062] To retain the concerned 50 Hz frequency band, the corner frequency can be taken as 150 Hz, that is, . Solving gives .

[0063] It should be noted that since the grid-forming control without a current inner loop has no direct measure to limit the current, it is necessary to consider that in a slight fault (the actual AC voltage is greater than and less than the lower limit of the normal operation of the AC voltage ), the actual AC current does not immediately reach the overcurrent setting value. If the virtual impedance is only activated by current overlimit at this time, it will cause the virtual impedance to be repeatedly switched on and off, which is not conducive to the steady-state operation during slight faults. Therefore, an AC voltage criterion is added at this time, that is, in a slight fault, the virtual impedance is activated through the voltage criterion to avoid the repeated switching on and off of the virtual impedance. In a severe fault (the actual AC voltage is less than ), the current instantaneous value criterion will quickly activate the virtual impedance to limit the current. Since the voltage criterion needs to calculate the positive sequence component or the effective value, the calculation time is longer than that of the current instantaneous value, which is not conducive to current limiting at the moment of fault occurrence.

[0064] The voltage drop generated by the virtual impedance is specifically:

[0065]

[0066]

[0067] The final modulation wave is:

[0068]

[0069]

[0070] Among them, , , .

[0071] 、 is the amplitude and phase angle of the internal electromotive force generated by the power outer loop; , , is the instantaneous value of the actual alternating current; , , is the voltage drop of the virtual impedance in the three-phase stationary coordinate system; , , is the final modulation wave in the three-phase stationary coordinate system.

[0072] It should be noted that since the present invention adopts the three-phase stationary coordinate system, the voltage drop generated by the virtual impedance is generated according to the three-phase actual current. When an asymmetric fault occurs, there will also be a modulation voltage corresponding to the negative sequence component in the finally reflected modulation wave. Therefore, the current limiting method provided by the present invention also has a certain limiting effect on the negative sequence component.

[0073] Compared with the prior art, the method of the embodiment of the present invention, including the fast current limiting method using the virtual impedance, mainly superimposes the virtual voltage drop corresponding to the virtual impedance on the three-phase internal electromotive force voltage as the final modulation wave. The value of the virtual impedance is determined by the actual hardware overcurrent capacity. The calculation of the virtual reactance is realized by an advanced adjustment link. The virtual impedance switching criterion combines the instantaneous value of the alternating current with the positive sequence modulus or effective value of the alternating voltage. By adding the measure of the virtual impedance in the three-phase stationary coordinate system, for equipment with limited overcurrent capacity, the current limiting measure implemented in this coordinate system does not require a filtering link. In case of a severe fault, the virtual impedance is started by using the instantaneous value of the current or the voltage criterion, so that the current limiting function can be realized more quickly; at the same time, the stable operation in case of a minor fault is also considered, and the modulus or effective value criterion of the positive sequence component of the voltage is added to start the virtual impedance criterion to avoid the repeated switching of the virtual impedance; since the present invention adopts the three-phase stationary coordinate system, the virtual impedance can limit the current within the overcurrent capacity of the equipment for both symmetrical and asymmetrical fault conditions.

[0074] Next, the network-forming control device of the voltage source type power electronic device provided by the present invention will be described. The network-forming control device of the voltage source type power electronic device described below can be mutually corresponding and referred to the network-forming control method of the voltage source type power electronic device described above.

[0075] Figure 4 is a schematic structural diagram of the network-forming control device of the voltage source type power electronic device provided by the present invention, which specifically includes: A judgment module 401, configured to judge the fault level when a fault occurs in the target power grid. For detailed description, please refer to the relevant description corresponding to the above method embodiment, which will not be elaborated here.

[0076] A determination module 402, configured to determine a starting judgment strategy for the virtual impedance based on the fault level. For detailed description, please refer to the relevant description corresponding to the above method embodiment, which will not be elaborated here.

[0077] A control module 403, configured to start the virtual impedance based on the starting judgment strategy, and perform network-forming control to limit current by using the virtual impedance in a three-phase static coordinate system, where the three-phase static coordinate system is the basis for network-forming control to limit the device current in the target power grid within the overcurrent capacity. For detailed description, please refer to the relevant description corresponding to the above method embodiment, which will not be elaborated here.

[0078] The control module 403 is further configured to control the voltage source type power electronic device to perform network-forming control on the target power grid in the state of network-forming control for current limiting. For detailed description, please refer to the relevant description corresponding to the above method embodiment, which will not be elaborated here.

[0079] Figure 5 An entity structure diagram of an electronic device is exemplified, as Figure 5 shown. The electronic device may include: a processor 810, a communication interface 820, a memory 830, and a communication bus 840. Among them, the processor 810, the communication interface 820, and the memory 830 communicate with each other through the communication bus 840. The processor 810 can call the logical instructions in the memory 830 to execute the network-forming control method of the voltage source type power electronic device. The method includes: when a fault occurs in the target power grid, judging the fault level; determining a starting judgment strategy for the virtual impedance based on the fault level; starting the virtual impedance based on the starting judgment strategy, and performing network-forming control to limit current by using the virtual impedance in a three-phase static coordinate system, where the three-phase static coordinate system is the basis for network-forming control to limit the device current in the target power grid within the overcurrent capacity; and controlling the voltage source type power electronic device to perform network-forming control on the target power grid in the state of network-forming control for current limiting.

[0080] In addition, when the logical instructions in the above-mentioned memory 830 can be implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0081] On the other hand, the present invention also provides a computer program product. The computer program product includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the network-forming control method of the voltage source type power electronic device provided by the above-mentioned various methods. The method includes: when a target power grid fails, judging the fault level; determining a starting judgment strategy for a virtual impedance based on the fault level; starting the virtual impedance based on the starting judgment strategy, and performing network-forming control current limiting using the virtual impedance in a three-phase stationary coordinate system, where the three-phase stationary coordinate system is the basis for network-forming control to limit the device current in the target power grid within the overcurrent capacity; and controlling the voltage source type power electronic device to perform network-forming control on the target power grid in the state of network-forming control current limiting.

[0082] On another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it is implemented to execute the network-forming control method of the voltage source type power electronic device provided by the above-mentioned various methods. The method includes: when a target power grid fails, judging the fault level; determining a starting judgment strategy for a virtual impedance based on the fault level; starting the virtual impedance based on the starting judgment strategy, and performing network-forming control current limiting using the virtual impedance in a three-phase stationary coordinate system, where the three-phase stationary coordinate system is the basis for network-forming control to limit the device current in the target power grid within the overcurrent capacity; and controlling the voltage source type power electronic device to perform network-forming control on the target power grid in the state of network-forming control current limiting.

[0083] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative efforts.

[0084] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the essence of the above technical solution, or the part that contributes to the prior art, can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or equivalently replace some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A grid-forming control method for a voltage-source power electronic device, characterized in that, Including: When a fault occurs in the target power grid, judge the fault level; Determine the starting judgment strategy of the virtual impedance based on the fault level; Start the virtual impedance based on the starting judgment strategy, and use the virtual impedance for grid-forming control to limit current in the three-phase static coordinate system, where the three-phase static coordinate system is the basis for grid-forming control to limit the device current in the target power grid within the overcurrent capacity; In the state of grid-forming control current limiting, control the voltage source type power electronic device to perform grid-forming control on the target power grid, and generate three-phase virtual voltages based on the virtual impedance to achieve the purpose of current limiting.

2. The method according to claim 1, characterized in that, The step of "When a fault occurs in the target power grid, judge the fault level" includes: Detect the instantaneous values of the three-phase AC currents and the modulus of the positive sequence components of the three-phase AC voltages of the target power grid; If the instantaneous value of the current is greater than or equal to the preset device overcurrent setting value or the modulus of the positive sequence component of the voltage is less than the positive sequence voltage setting value of the first-level fault, determine that the fault level is the first-level fault; Detect the effective values of the three-phase AC voltages of the target power grid; If the modulus of the positive sequence component of the voltage or the effective value of the voltage is between the lower limit of the normal operation of the target power grid and the preset positive sequence voltage or the effective value of the voltage, determine that the fault level is the second-level fault.

3. The method according to claim 1 or 2, characterized in that, The step of "Determine the starting judgment strategy of the virtual impedance based on the fault level" includes: If it is determined that the fault level is the first-level fault, immediately start the virtual impedance, and the starting judgment strategy is to start the virtual impedance through the instantaneous value of the current or the voltage criterion; If it is determined that the fault level is the second-level fault, the starting judgment strategy is to start the virtual impedance through the voltage criterion.

4. The method according to claim 3, wherein The step of "Start the virtual impedance based on the starting judgment strategy, and use the virtual impedance for grid-forming control to limit current in the three-phase static coordinate system" includes: After starting the virtual impedance, superimpose a virtual voltage drop on the potential voltage in the three-phase static coordinate system of the target power grid, and limit the current passing through the devices in the target power grid through the virtual voltage drop corresponding to the virtual impedance.

5. The method according to claim 4, wherein The step of "Limit the current passing through the devices in the target power grid through the virtual voltage drop corresponding to the virtual impedance" includes: Calculate the voltage drop generated by the virtual impedance; Determine the corresponding virtual voltage drop based on the voltage drop generated by the virtual impedance, and generate a target modulation wave based on the virtual voltage drop; Control the switching action of the voltage source type power electronic device based on the target modulation wave, and control the output current and voltage; Limit the current passing through the devices in the target power grid through the voltage output by the voltage source type power electronic device.

6. The method according to claim 5, wherein The method further includes: During the process of controlling the voltage source type power electronic device to perform grid-forming control on the target power grid, continuously monitor the changes in current and voltage; Dynamically adjust the virtual impedance based on the changes in current and voltage.

7. The method according to claim 1, wherein The method further includes: Determine the value of the virtual impedance based on the overcurrent capacity of the voltage source type power electronic device.

8. A grid-forming control device for a voltage-source power electronic device, characterized in that, Including: A judgment module, used to judge the fault level when a fault occurs in the target power grid; A determination module, used to determine the starting judgment strategy of the virtual impedance based on the fault level; A control module, configured to start the virtual impedance based on the startup judgment strategy, and perform network formation control for current limiting by using the virtual impedance in a three-phase static coordinate system, where the three-phase static coordinate system is the basis for the network formation control to limit the device current in the target power grid within the overcurrent capacity; The control module is further configured to, in a state of network formation control for current limiting, control the voltage source type power electronic device to perform network formation control on the target power grid.

9. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the network formation control method of the voltage source type power electronic device according to any one of claims 1 to 7.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the network formation control method of the voltage source type power electronic device according to any one of claims 1 to 7.

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