An emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetric grid faults

Abstract

The application discloses an emergency power control method for a hybrid flexible medium-voltage power flow transfer device under an asymmetric power grid fault, and belongs to the technical field of flexible power flow transfer of a medium-voltage distribution network. In view of the double problems that the power transmission capacity of the device is limited and the device is prone to entering an over-modulation state caused by an asymmetric power grid fault, the method can not only actively balance the modulation depth of each phase, constrain the modulation wave in a linear interval, but also preferentially maintain or urgently adjust active power under the fault condition by injecting a specific zero sequence voltage component into a three-phase modulation wave. Therefore, the emergency power control during the asymmetric fault is simultaneously realized without the need of improving the DC side voltage of the device or changing the main circuit structure, and the power regulation range and stable operation capacity of the device under the asymmetric fault condition are expanded.

Description

Technical Field

[0001] This invention relates to the field of flexible power flow transfer technology in medium-voltage distribution networks, and is an emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical grid faults. The proposed method overcomes the problem of overmodulation that power flow transfer devices are prone to under asymmetrical grid fault conditions. By injecting a zero-sequence voltage component into the output voltage modulation wave, the safe operating range of the device is effectively extended without increasing hardware costs, realizing emergency power control of the device under asymmetrical grid faults. It is suitable for low-cost, high-efficiency flexible power flow control in medium-voltage distribution networks. Background Technology

[0002] With the large-scale grid connection of distributed energy and the widespread application of flexible AC transmission technology, flexible power flow transfer devices based on power electronics technology in medium-voltage distribution networks have become key equipment for improving system flexibility and controllability. Under normal grid voltage conditions, the amplitude and phase angle difference between the voltages at both ends of the grid are small, and the output voltage of the device is approximately equal to this voltage difference. At this time, the device operates within the linear modulation zone and can accurately regulate the power flow of the line. However, when an asymmetrical fault such as a short circuit or voltage drop occurs on one side of the grid, the system voltage becomes unbalanced in three phases, and the amplitude and phase difference between the grids on both sides of the device increases sharply. This can easily cause the modulation signal of one phase to exceed the physical output range, leading to overmodulation. Overmodulation not only introduces a large number of low-order harmonics and degrades power quality, but may also cause the device protection to activate or shut down, interrupting power exchange between substations. Especially in topologies such as modular multilevel or cascaded H-bridges, overmodulation can further induce uneven voltage in submodules, capacitor oscillations, and even device breakdown, seriously threatening the safety and stability of the system. To address the aforementioned issues, traditional solutions to overmodulation problems primarily focus on optimizing the modulation algorithm or increasing the DC-side voltage margin. While the former can extend the linear modulation region to a limited extent, it still introduces a large number of low-order harmonics during deep overmodulation, affecting power quality and grid-connected equipment safety. The latter requires increasing the DC capacitor voltage level or the number of power modules, resulting in a significant increase in device size, cost, and losses, making it less economical.

[0003] Therefore, developing a control method that can effectively prevent over-modulation and perform emergency power control under asymmetrical grid faults without relying on hardware upgrades has become a key technology for improving the safety and adaptability of flexible power flow transfer devices, and is of great significance for ensuring the safe and high-quality operation of the distribution network. Summary of the Invention

[0004] This invention proposes an emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults, belonging to the technical field of flexible power flow transfer technology for medium-voltage distribution networks. The device consists of an active module and a suspended module. The suspended module is responsible for reactive power regulation, while the active module is responsible for active power regulation and reactive power regulation exceeding the capacity of the suspended module.

[0005] When a single-phase voltage dip fault occurs in the power grid, this method actively adjusts and balances the modulation depth of each phase by injecting a specific zero-sequence voltage component into the three-phase modulation wave. This reduces the voltage amplitude of the phase with an excessively high modulation ratio while moderately increasing the amplitude of the modulation waves of the other two phases. This ensures that the three-phase modulation wave of the device remains within the linear modulation range under single-phase dip fault conditions. Thus, without increasing the DC-side voltage or changing the main circuit structure, the device maintains its predetermined power flow transfer capability and effectively extends its stable operating range under fault conditions. The method proposed in this invention effectively expands the safe operating domain of the device without increasing hardware costs, and is suitable for low-cost, high-efficiency, and flexible power flow control in medium-voltage distribution networks.

[0006] This invention is achieved through the following technical solution:

[0007] According to claim 1, the voltage of the medium-voltage power grid 1 is measured by the voltage sensor. , No. i DC voltage of each active module , No. j DC voltage of each floating module The voltage of medium-voltage power grid 2 Output voltage of the power supply device According to claim 1, the current sensor measures the first... i The current of each active module in parallel unit and line transmission current ; The controller obtains the voltage from grid 1 via a phase-locked loop. phase Line current phase Device output voltage amplitude and phase Based on the phase of the line current For the device output voltage Orientation is performed to obtain the amplitude of its active component. With reactive component amplitude ; The device receives the active power reference value to be transferred. and reactive power reference value A dual-loop controller, consisting of a power outer loop and a current inner loop, is used to control the actual power supplied. and Precise control is achieved to obtain the device's power command voltage reference. ; The active module rectifier controller collects the first... i DC capacitor voltage of each active module The parallel unit current reference is generated by the DC voltage outer loop control, and then adjusted by the current inner loop controller to obtain the first... i The modulated wave voltage of a parallel unit of an active module; The pressure equalization controller of the suspension module collects the first... j DC capacitor voltage of each floating module By controlling the DC voltage, the first... j Each suspended module modulates the wave voltage; The zero-sequence voltage injection controller determines the operating boundary of the active component of the device's output voltage based on the magnitude of the DC-side voltages of the active module and the floating module. R d Operating boundary with reactive components R q ; The zero-sequence voltage injection controller measures the amplitude of the active component of the device's output voltage. With reactive component amplitude By comparing it with its corresponding boundary, we obtain d Axial direction and q Axial direction over-limit flag , The flag determines whether to inject a zero-sequence voltage component in the corresponding direction. Subsequently, when the device output voltage exceeds the limit, the corresponding boundary is used as a reference value. The proportional-integral controller then obtains the zero-sequence voltage amplitude, thereby generating the zero-sequence voltage reference for each phase. Finally, the three-phase zero-sequence voltage components are added together to obtain the final zero-sequence voltage reference. ; The reference voltage generation stage for the active module and the levitation module will generate the power command voltage reference. Zero-sequence voltage reference Obtain the device's total voltage reference Then, through a phase-locked loop, the phase of the line current is determined. Based on the reference value of the total voltage of the device The active component amplitude is obtained by decomposition. With reactive component amplitude Finally, following the principle that the suspended module should bear the reactive voltage component to the maximum extent, and the active module should bear the remaining reactive voltage component and all active voltage components, the final voltage reference signals of the active module and the suspended module are calculated and generated respectively. The controller generates a switching drive signal for the active module by sinusoidal pulse width modulation of the active module voltage reference signal; and generates a switching drive signal for the floating module by superimposing the floating module voltage reference signal and its equalizing signal by sinusoidal pulse width modulation.

[0008] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: 1. The electrical connection structure of the hybrid flexible medium-voltage power flow transfer device proposed in this invention supports flexible splicing and expansion in both hardware topology and control strategy, and can adapt to distribution network application scenarios of different voltage levels, greatly improving the device's scenario adaptability and application flexibility. 2. The present invention proposes an emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical grid faults. In terms of control strategy, it realizes zero-sequence voltage adaptive injection, which can cope with grid voltage fault scenarios with different voltage drop levels, and greatly improve the operational safety and control robustness of the device under fault transients. 3. The emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults proposed in this invention is based entirely on software algorithm upgrades when realizing the extended operation domain function. It does not require additional hardware costs or changes to the main circuit topology, which greatly improves the economy of device technology upgrades and the convenience of engineering implementation. Attached Figure Description

[0009] Figure 1 An electrical connection structure diagram of a hybrid flexible medium-voltage power transfer device provided in an embodiment of the present invention; Figure 2 A control architecture diagram of an emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults, provided in an embodiment of the present invention; Figure 3 A flowchart of an emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults, provided in an embodiment of the present invention; Figure 4 Equivalent circuit diagram of a medium-voltage power grid flexible power flow transfer system provided in an embodiment of the present invention; Figure 5 A vector diagram of the main electrical quantities of a medium-voltage power grid flexible power flow transfer system provided in an embodiment of the present invention; Figure 6A detailed control block diagram of an emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults, provided for an embodiment of the present invention; Figure 7 A schematic diagram of the operating boundary of the three-phase voltage of the hybrid flexible medium-voltage power supply device provided in an embodiment of the present invention; Figure 8 Schematic diagrams of three overmodulation conditions of the hybrid flexible medium-voltage power transfer device provided in the embodiments of the present invention; Figure 9 The three-phase voltage amplitude and power curves of the receiving-end power grid under various operating conditions are provided in the embodiments of the present invention. Figure 10 This is a three-phase voltage over-limit flag provided in an embodiment of the present invention; Figure 11 The curves showing the variation of the fundamental total amplitude, active component amplitude, and reactive component amplitude of the output voltage of the hybrid flexible medium-voltage power transfer device provided in this embodiment of the invention; Figure 12 The voltage modulation signals and actual output PWM voltage waveforms of the active and passive modules of the hybrid flexible medium-voltage power transfer device provided in the embodiments of the present invention; Figure 13 The zero-sequence voltage reference waveform provided in the embodiments of the present invention; Figure 14 This is a schematic diagram of the device output voltage vector under various operating conditions provided in the embodiments of the present invention; Figure 15 A schematic diagram of a module for an emergency power control method of a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults, provided by an embodiment of the present invention; Figure 16 This is a schematic diagram of a hybrid flexible medium-pressure power transfer device provided in an embodiment of the present invention. Detailed Implementation

[0010] To more clearly illustrate the purpose, technical solution, and advantages of this application, the following detailed description will be provided with reference to the accompanying drawings and specific examples. In this application, the described method embodiments can also be applied to the implementation of an apparatus or system. It should be noted that in the description of this application, "at least one" refers to one or more, where "multiple" refers to two or more. Therefore, in the embodiments of this application, "multiple" can also be understood as "at least two." "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / ", unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are only used for distinguishing the descriptive purpose and should not be construed as indicating or implying relative importance or order. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0011] Please refer to Figure 1 An electrical connection structure for a hybrid flexible medium-voltage power transfer device, characterized in that it includes: a transformer, an active module, a levitation module, a current sensor, a voltage sensor, and controllers for each module; The active module includes m series units and parallel units. One end of the parallel unit is connected to the medium-voltage power grid 1 through the transformer, and the other end is connected to the DC capacitor of the active module. One end of the series unit is connected to the DC capacitor of the active module, and the other end is connected in series between the medium-voltage power grid 1 and the floating module. The levitation module includes n power converters and corresponding DC levitation capacitors.

[0012] The first voltage sensor is installed in the medium-voltage power grid 1, the first current sensor is installed between the transformer and the parallel unit of the active module, the second voltage sensor is installed at both ends of the DC capacitor of the active module, the second current sensor is installed in the line, the third voltage sensor is installed at both ends of the DC capacitor of the floating module, the fourth voltage sensor is installed in the medium-voltage power grid 2, and the fifth voltage sensor is installed at both ends of the power flow conversion device. Please refer to Figure 2 A control architecture diagram of an emergency power control method for a hybrid flexible medium-voltage power transfer device under asymmetrical grid faults, and Figure 3 A schematic diagram illustrating the implementation process of an emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical grid faults, including: Step S301: Measure the voltage of the medium-voltage power grid 1 using the voltage sensor according to claim 1. , No.i DC voltage of each active module , No. j DC voltage of each floating module The voltage of medium-voltage power grid 2 Output voltage of the power supply device According to claim 1, the current sensor measures the first... i The current of each active module in parallel unit and line transmission current ; Please refer to Figure 4 The equivalent circuit diagram of the flexible power flow transfer system provided in the embodiments of the present invention, and Figure 5 The vector diagram of the main electrical quantities of the flexible power flow transfer system provided in this embodiment of the invention can help in understanding... Figure 6 The dq-axis components of the modulation voltage; Please refer to Figure 6 A detailed control block diagram of an emergency power control method for a hybrid flexible medium-voltage power transfer device under asymmetrical grid faults, step S302: The controller obtains the grid voltage 1 through a phase-locked loop. phase Line current phase Device output voltage amplitude and phase Based on the phase of the line current For the device output voltage Orientation is performed to obtain the amplitude of its active component. With reactive component amplitude As shown in the following formula: (1)

[0013] Step S303: The device receives the reference value of the active power to be transferred. and reactive power reference value A dual-loop controller, consisting of a power outer loop and a current inner loop, is used to control the actual power supplied. and Precise control is achieved to obtain the device's power command voltage reference. As shown in the following formula: (2) In the formula, , These are the proportional and integral coefficients of the power closed-loop controller, respectively. , The respective line transmission current dqAxis reference. The line-transmitted current is referenced to the phase of power grid 1. dq Instantaneous value reference obtained by axis transformation: (3) Then, the line current is regulated in a closed loop using a PR controller, and the voltage difference between the two grid terminals is introduced as feedforward: (4) In the formula, This is the reference value for the total voltage of the power flow regulation device. and These are the proportional coefficient and resonant coefficient of the current controller, respectively. For controller bandwidth, This is the reference frequency.

[0014] Step S304: The active module rectifier controller acquires the first... i DC capacitor voltage of each active module The parallel unit current reference is generated by the DC voltage outer loop control, and then adjusted by the current inner loop controller to obtain the first... i The modulated wave voltage of the parallel active module unit is shown in the following formula: (5) In the formula, The voltage phase of grid 1, and These are the proportional and integral coefficients of the DC voltage controller for the parallel unit.

[0015] Then, receive the AC port current of the parallel unit. The first current loop controller is used to obtain the second current loop controller. i The modulated wave voltage of the parallel unit of the active module is shown in the following formula: (6) in, and These are the proportional coefficient and resonant coefficient of the current controller for the parallel unit, respectively. Finally, the first [unit] is obtained through SPWM modulation. i The switching signals of the parallel active module units.

[0016] Step S305: The suspension module pressure equalization controller collects the first... j DC capacitor voltage of each floating module The first is obtained by controlling the DC voltage. j The amplitude of the modulated wave voltage of each suspended module, multiplied by , obtained the j The modulated wave voltage of the floating module is shown in the following formula: (7) In the formula, The voltage phase of grid 1, and These are the proportional and integral coefficients of the equalizing controller for the suspension module.

[0017] Please refer to Figure 7 The schematic diagram of the operating boundary of the three-phase voltage of the hybrid flexible medium-voltage power supply device provided in this embodiment of the invention can help to understand the determination of the operating boundary in step S306.

[0018] Please refer to Figure 8 The schematic diagrams of three overmodulation conditions of the hybrid flexible medium-voltage power supply device provided in this embodiment of the invention can help to understand the values ​​of the overlimit flag bit under different conditions in step S306.

[0019] Step S306: The zero-sequence voltage injection controller determines the operating boundary of the active component of the device output voltage based on the magnitude of the DC-side voltages of the active module and the floating module. R d Operating boundary with reactive components R q As shown in the following formula: (8) In the formula, m is the number of active modules and n is the number of floating modules.

[0020] The zero-sequence voltage injection controller measures the amplitude of the active component of the device's output voltage. With reactive component amplitude By comparing it with its corresponding boundary, we obtain d Axial direction and q Axial direction over-limit flag , The decision to inject a zero-sequence voltage component in the corresponding direction is based on this flag, as shown in the following formula: (9) Subsequently, when the device output voltage exceeds the limit, the boundary is used as a reference value, and the zero-sequence voltage amplitude is calculated by the proportional-integral controller to obtain the zero-sequence voltage reference for each phase, as shown in the following formula: (10) In the formula, As the zero-sequence voltage reference for each phase, x =a, b, c.

[0021] Finally, the three-phase zero-sequence voltage components are summed to obtain the final zero-sequence voltage reference. As shown in the following formula: (11)

[0022] Step S307: In the reference voltage generation process for the active module and the floating module, based on the power voltage reference... Zero-sequence voltage reference Obtain the device's total voltage reference As shown in the following formula: (12) Then, through a phase-locked loop, the phase of the line current is determined. Based on the total output voltage of the device Decompose the active component to obtain its amplitude. With reactive component amplitude ; Finally, following the principle of maximizing the utilization of the active module and using the floating module as the remaining voltage reference, the voltage reference signals for the active and floating modules are obtained, as shown in the following formula: (13) In the formula, , These are the reference signals for the suspending module and the active module, respectively.

[0023] Step S308: The controller generates a switching drive signal for the active module by sinusoidal pulse width modulation of the active module voltage reference signal; and generates a switching drive signal for the floating module by superimposing the floating module voltage reference signal and its equalization signal by sinusoidal pulse width modulation.

[0024] Figure 9 This document illustrates the three-phase voltage amplitude and power curves of the receiving-end power grid under various operating conditions provided in the embodiments of the present invention. The list of operating conditions is as follows: Figure 9 As shown in (a); Figure 9 (b) shows the voltage amplitude and power of grid 2 (receiving end grid). It can be seen that the voltage of phase C of grid 2 drops to 0.4pu in 0.2s; the power of the receiving end changes continuously in operating conditions 2 to 6 to create different voltage over-modulation conditions.

[0025] Figure 10 The embodiments of the present invention demonstrate the voltage over-limit flags for each phase. When the flag is 1, it indicates that the voltage component exceeds the limit in the positive direction; when the flag is -1, it indicates that the voltage component exceeds the limit in the negative direction; and when the flag is 0, it indicates that the voltage component does not exceed the limit. It can be seen that after each change in the power supplied by the 0.2sC voltage, a voltage over-limit occurs, but the proposed control method can respond quickly and limit it within the linear modulation range.

[0026] Figure 11The curves showing the variation of the fundamental total amplitude, active component amplitude, and reactive component amplitude of the output voltage of the hybrid flexible medium-voltage power transfer device provided in the embodiments of the present invention are displayed. It can be seen that the output voltage of the device can be well constrained within the linear modulation range each time the power changes.

[0027] Figure 12 The voltage modulation signals and actual output PWM voltage waveforms of the active and passive modules of the hybrid flexible medium-voltage power transfer device provided in this embodiment of the invention are shown. It can be seen that when the voltage of phase 2C of the power grid drops, the voltage modulation waveform of the active module and the output PWM voltage exhibit clipping due to overmodulation. When emergency power control is enabled, the overmodulation phenomenon is suppressed.

[0028] Figure 13 The waveform of the injected zero-sequence voltage reference provided by the embodiment of the present invention is shown; when emergency power control is enabled, a zero-sequence voltage reference begins to be generated, and the zero-sequence voltage reference is adjusted in real time under different operating conditions.

[0029] Figure 14 The diagram shows the trajectory of the injected zero-sequence voltage under various operating conditions provided by the embodiments of the present invention, intuitively demonstrating the change trajectory of the injected zero-sequence voltage under various operating conditions.

[0030] This invention is not limited to the embodiments described above. The above description of specific embodiments is intended to illustrate and explain the technical solutions of this invention. The specific embodiments described above are merely illustrative and not restrictive. Without departing from the spirit and scope of the claims, those skilled in the art can make many specific modifications based on the teachings of this invention, and these modifications all fall within the scope of protection of this invention.

[0031] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0032] Example module Figure 15 As shown, an emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical grid faults includes: The sampling module 1501 is used to obtain the grid voltage, device output voltage, device DC voltage and line current based on the sensor. The power calculation module 1502 is used to obtain the active and reactive components of the device output voltage through a phase-locked loop based on the device output voltage and line current. The power command determination module 1503 is used to determine the power voltage reference signal according to the power command; The active module voltage equalization signal determination module 1504 is used to determine the voltage equalization modulation wave of the parallel unit of the active module based on the DC voltage of the device and through the DC voltage controller. The suspension module equalization signal determination module 1505 is used to determine the suspension module equalization modulation wave based on the device's DC voltage and through a DC voltage controller. The zero-sequence voltage reference determination module 1506 is used to determine the voltage boundary and zero-sequence voltage reference for device operation based on the device output voltage and the device DC voltage. The modulation signal determination module 1507 is used to determine the modulation signals of the active module and the passive module based on the first determination module and the fourth determination module.

[0033] The drive signal acquisition module 1508 is used to determine the switching drive signals of the active module and the passive module of the device according to the fifth determination module.

[0034] Figure 16 A schematic diagram of a hybrid flexible medium-pressure power transfer device provided by an embodiment of the present invention is shown.

[0035] A schematic diagram of the hybrid medium-pressure flexible power transfer device is shown below. Figure 16 As shown, it includes: a power conversion circuit 1601, a controller 1602, a memory 1603, and a computer program 1604 stored in the memory 1603 and executable on the controller 1602. When the controller 1602 executes the computer program 1604, it implements the steps in the voltage compensation method embodiments described above, for example... Figure 3 The steps S301 to S308 are shown. Alternatively, when the controller 1602 executes the computer program 1604, it implements the power of each module / unit in the above embodiments, for example... Figure 15 The functions of modules 1501 to 1508 are shown.

[0036] For example, the computer program 1604 can be divided into one or more modules / units, which are stored in the memory 1603 and executed by the controller 1602 to complete the embodiments of the present invention. The one or more modules / units can be a series of computer program instruction segments capable of performing specific functions, which describe the execution process of the computer program 1604 in the single-phase power electronic voltage regulator 16. For example, the computer program 1604 can be divided into a first obtaining module, a second obtaining module, a first determining module, a second determining module, a third determining module, a fourth determining module, a fifth determining module, and a third obtaining module, with the functions of each module as follows: The sampling module is used to obtain the grid voltage, device output voltage, device DC voltage and line current based on the sensor. The power calculation module is used to obtain the active and reactive components of the device's output voltage through a phase-locked loop based on the device's output voltage and line current. The power command determination module is used to determine the power voltage reference signal based on the power command. The active module voltage equalization signal determination module is used to determine the voltage equalization modulation wave of the parallel unit of the active module based on the DC voltage of the device and through the DC voltage controller. The suspension module voltage equalization signal determination module is used to determine the suspension module voltage equalization modulation wave based on the device's DC voltage and through a DC voltage controller. The zero-sequence voltage reference determination module is used to determine the operating voltage boundary and zero-sequence voltage reference of the device based on the device output voltage and the device DC voltage. The modulation signal determination module is used to determine the modulation signals of the active module and the passive module based on the first determination module and the fourth determination module.

[0037] The drive signal acquisition module is used to determine the switching drive signals of the active module and the passive module of the device according to the fifth determination module.

[0038] The emergency power control method for the hybrid flexible medium-voltage power flow transfer device under asymmetrical grid faults may include, but is not limited to, a main circuit 1601, a controller 1602, and a memory 1603. Those skilled in the art will understand that... Figure 16 This is merely an example of the hybrid flexible medium-voltage power transfer device 16 and does not constitute a limitation on the hybrid flexible medium-voltage power transfer device. It may include more or fewer components than shown in the figure, or combine certain components, or different components. For example, the number of active modules and floating modules in the main circuit does not necessarily have to be only two each, and can be designed to be any number depending on the specific scenario.

[0039] The controller 1602 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0040] The memory 1603 can be an internal storage unit of the hybrid flexible medium-voltage power transfer device 16, such as an external storage circuit of the power electronic voltage regulator 16. Examples include plug-in hard drives, smart media cards (SMC), secure digital (SD) cards, and flash cards equipped on the hybrid flexible medium-voltage power transfer device 16. Furthermore, the memory 1603 can include both internal storage units and external storage devices. The memory 1603 is used to store the emergency power control algorithm and other programs and data required by the hybrid flexible medium-voltage power transfer device. The memory 1603 can also be used to temporarily store data that has been output or will be output.

[0041] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0042] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0043] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0044] In the embodiments provided by this invention, it should be understood that the disclosed apparatus / terminal devices and methods can be implemented in other ways. For example, the apparatus / terminal device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0045] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some units can be selected to achieve the purpose of this embodiment according to actual needs.

[0046] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0047] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0048] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A hybrid flexible medium-voltage power transfer device, characterized in that, include: Transformer, active module, floating module, current sensor, voltage sensor and controllers for each module; The active module includes m series units and parallel units. One end of the parallel unit is connected to the medium-voltage power grid 1 through the transformer, and the other end is connected to the DC capacitor of the active module. One end of the series unit is connected to the DC capacitor of the active module, and the other end is connected in series between the medium-voltage power grid 1 and the floating module. The levitation module includes n power converters and corresponding DC levitation capacitors; The first voltage sensor is installed in the medium-voltage power grid 1, the first current sensor is installed between the transformer and the parallel unit of the active module, the second voltage sensor is installed across the DC capacitor of the active module, the second current sensor is installed in the line, the third voltage sensor is installed across the DC capacitor of the floating module, the fourth voltage sensor is installed in the medium-voltage power grid 2, and the fifth voltage sensor is installed across the power flow conversion device.

2. An emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults, characterized in that, include: According to claim 1, the voltage of the medium-voltage power grid 1 is measured by the voltage sensor. , No. i DC voltage of each active module , No. j DC voltage of each floating module The voltage of medium voltage power grid 2 Output voltage of the power supply device ; According to claim 1, the current sensor measures the first... i The current of each active module in parallel unit and line transmission current ; The controller obtains the voltage from grid 1 via a phase-locked loop. phase Line current phase Device output voltage amplitude and phase Based on the phase of the line current For the device output voltage Orientation is performed to obtain the amplitude of its active component. With reactive component amplitude ; The device receives the active power reference value to be transferred. and reactive power reference value A dual-loop controller, consisting of a power outer loop and a current inner loop, is used to control the actual power supplied. and Precise control is achieved to obtain the device's power command voltage reference. ; The active module rectifier controller collects the first... i DC capacitor voltage of each active module The parallel unit current reference is generated by the DC voltage outer loop control, and then adjusted by the current inner loop controller to obtain the first... i The modulated wave voltage of a parallel unit of an active module; The pressure equalization controller of the suspension module collects the first... j DC capacitor voltage of each floating module By controlling the DC voltage, the first... j Each suspended module modulates the wave voltage; The zero-sequence voltage injection controller determines the operating boundary of the active component of the device's output voltage based on the magnitude of the DC-side voltages of the active module and the floating module. R d Operating boundary with reactive components R q ; The zero-sequence voltage injection controller measures the amplitude of the active component of the device's output voltage. With reactive component amplitude By comparing it with its corresponding boundary, we obtain d Axial direction and q Axial direction over-limit flag , The flag determines whether to inject a zero-sequence voltage component in the corresponding direction. Subsequently, when the device output voltage exceeds the limit, the corresponding boundary is used as a reference value, and the zero-sequence voltage amplitude is obtained through a proportional-integral controller, thereby generating the zero-sequence voltage reference for each phase. Finally, the three-phase zero-sequence voltage components are added together to obtain the final zero-sequence voltage reference. ; The reference voltage generation stage for the active module and the levitation module will generate the power command voltage reference. Zero-sequence voltage reference Obtain the device's total voltage reference ; Then, through a phase-locked loop, the phase of the line current is determined. Based on the reference value of the total voltage of the device The active component amplitude is obtained by decomposition. With reactive component amplitude Finally, following the principle that the floating module should bear the reactive voltage component to the maximum extent, and the active module should bear the remaining reactive voltage component and all active voltage components, the final voltage reference signals of the active module and the floating module are calculated and generated respectively. The controller modulates the active module voltage reference signal with a sinusoidal pulse width to generate a switching drive signal for the active module. The voltage reference signal of the floating module is superimposed on its equalization signal, and then sinusoidal pulse width modulation is applied to generate the switching drive signal of the floating module.

3. The emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults according to claim 2, characterized in that: According to claim 1, the voltage of the medium-voltage power grid 1 is measured by the voltage sensor. , No. i DC voltage of each active module , No. j DC voltage of each floating module The voltage of medium voltage power grid 2 Output voltage of the power supply device ; According to claim 1, the current sensor measures the current of the parallel unit of the active module. and line transmission current .

4. The emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults according to claim 2, characterized in that: The controller obtains the voltage from grid 1 via a phase-locked loop. phase Line current phase Device output voltage amplitude and phase Based on the phase of the line current For the device output voltage Orientation is performed to obtain the amplitude of its active component. With reactive component amplitude As shown in the following formula: (1)。 5. The emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults according to claim 2, characterized in that: The device receives the active power reference value to be transferred. and reactive power reference value A dual-loop controller, consisting of a power outer loop and a current inner loop, is used to control the actual power supplied. and Precise control is achieved to obtain the device's power command voltage reference. As shown in the following formula: (2) In the formula, , These are the proportional and integral coefficients of the power closed-loop controller, respectively. , The respective line transmission current dq Axis reference. The line-transmitted current is referenced to the phase of power grid 1. dq Instantaneous value reference obtained by axis transformation: (3) Then, the line current is regulated in a closed loop using a PR controller, and the voltage difference between the two grid terminals is introduced as feedforward: (4) In the formula, This is the reference value for the total voltage of the power flow regulation device. and These are the proportional coefficient and resonant coefficient of the current controller, respectively. For controller bandwidth, This is the reference frequency.

6. The emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults according to claim 2, characterized in that: The active module rectifier controller collects the first... i DC capacitor voltage of each active module The parallel unit current reference is generated by the DC voltage outer loop control, and then adjusted by the current inner loop controller to obtain the first... i The modulated wave voltage of the parallel active module unit is shown in the following formula: (5) In the formula, The voltage phase of grid 1, and For the proportional and integral coefficients of the DC voltage controller of the parallel unit; Then, receive the AC port current of the parallel unit. The first current loop controller is used to obtain the second current loop controller. i The modulated wave voltage of the parallel unit of the active module is shown in the following formula: (6) in, and These are the proportional coefficient and resonant coefficient of the current controller for the parallel unit, respectively. Finally, the first [unit] is obtained through SPWM modulation. i The switching signals of the parallel active module units.

7. The emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults according to claim 2, characterized in that: The pressure equalization controller of the suspension module collects the first... j DC capacitor voltage of each floating module The first is obtained by controlling the DC voltage. j The amplitude of the modulated wave voltage of each suspended module, multiplied by , obtained the j The modulated wave voltage of the floating module is shown in the following formula: (7) In the formula, The voltage phase of grid 1, and These are the proportional and integral coefficients of the equalizing controller for the suspension module.

8. The emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults according to claim 2, characterized in that: The zero-sequence voltage injection controller determines the operating boundary of the active component of the device's output voltage based on the magnitude of the DC-side voltages of the active module and the floating module. R d Operating boundary with reactive components R q As shown in the following formula: (8) In the formula, m is the number of active modules and n is the number of floating modules; The zero-sequence voltage injection controller measures the amplitude of the active component of the device's output voltage. With reactive component amplitude By comparing it with its corresponding boundary, we obtain d Axial direction and q Axial direction over-limit flag , The decision to inject a zero-sequence voltage component in the corresponding direction is based on this flag, as shown in the following formula: (9) Subsequently, when the device output voltage exceeds the limit, the boundary is used as a reference value, and the zero-sequence voltage amplitude is calculated by the proportional-integral controller to obtain the zero-sequence voltage reference for each phase, as shown in the following formula: (10) In the formula, As the zero-sequence voltage reference for each phase, x =a, b, c, and The proportional and integral coefficients of the zero-sequence voltage injection controller; Finally, the three-phase zero-sequence voltage components are summed to obtain the final zero-sequence voltage reference. As shown in the following formula: (11)。 9. The emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults according to claim 2, characterized in that: In the reference voltage generation process for the active module and the levitation module, based on the power voltage reference... Zero-sequence voltage reference Obtain the device's total voltage reference As shown in the following formula: (12) Then, through a phase-locked loop, the phase of the line current is determined. Based on the total output voltage of the device Decompose the active component to obtain its amplitude. With reactive component amplitude ; Finally, following the principle of maximizing the utilization of the active module and using the floating module as the remaining voltage reference, the voltage reference signals for the active and floating modules are obtained, as shown in the following formula: (13) In the formula, , These are the reference signals for the levitation module and the active module, respectively. It is a symbolic function.

10. The emergency power control method for a hybrid flexible medium-voltage power flow transfer device under asymmetrical power grid faults according to claim 2, characterized in that: The controller modulates the active module voltage reference signal with a sinusoidal pulse width to generate a switching drive signal for the active module. The voltage reference signal of the floating module is superimposed on its equalization signal, and then sinusoidal pulse width modulation is applied to generate the switching drive signal of the floating module.

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