Capacitive coupling type low-cost medium-voltage flexible power flow transfer device and control method

Abstract

The invention provides a capacitive coupling type low-cost medium-voltage flexible power flow transfer device and a control method, and belongs to the technical field of power distribution network flexible power flow transfer. Each phase of circuit of the device comprises a three-bridge-arm power module, a parallel port filter inductor, a series port filter inductor, a filter capacitor and a medium-voltage capacitor bank. The reactive current of the medium-voltage capacitor is coupled with the output voltage of the first bridge arm and the second bridge arm of the three-bridge-arm parallel port so as to maintain the stability of the direct-current bus, and the power flow regulation is realized through the control of the second bridge arm and the third bridge arm of the series port. In order to make full use of the capacity of the converter, the invention provides a self-adaptive segmented switching method for a capacitor bank, and on the premise of keeping the direct current voltage stable, the modulation ratio of a parallel port is maintained in a relatively high interval, so that the current resistance stress of a device is reduced. The UPFC circuit has the advantages of being free of isolation change, compact in structure, low in cost, small in parallel branch current and the like, compared with a traditional UPFC circuit, the capacity of a power device is further reduced, and the economical efficiency of the system is improved.

Description

Technical Field

[0001] This invention relates to the field of flexible power flow regulation technology for medium-voltage distribution networks, and is a low-cost medium-voltage flexible power flow transfer device and control method that also takes into account reactive power compensation capabilities. The proposed medium-voltage flexible power flow transfer device does not require isolation transformers and numerous power electronic devices, and is suitable for low-cost, high-efficiency flexible power flow transfer in medium-voltage distribution networks. Background Technology

[0002] With the large-scale integration of distributed photovoltaic and other renewable energy sources into the grid, problems such as severe imbalances in line load rates, voltage exceeding limits, and disordered power flow distribution have gradually emerged in the distribution network. These problems not only degrade power quality but may also trigger equipment failures and even threaten the safe and stable operation of the entire distribution network. Without altering the existing power system grid structure, using flexible power electronic devices to achieve flexible power flow transfer between different distribution substations has become an effective method to solve these problems. Such devices can transfer a portion of the power from high-load substations to low-load substations, promoting local balance and absorption of renewable energy within the substation area, and fundamentally alleviating the grid operation pressure brought about by the large-scale integration of renewable energy.

[0003] To address the aforementioned issues, developing efficient and economical flexible power flow transfer devices has become a crucial research direction in the field of distribution network optimization. However, current mainstream flexible power flow transfer devices suffer from significant technical shortcomings. Traditional solutions primarily employ a full-power back-to-back circuit topology. This structure requires a converter to process all flowing power, resulting in large converter capacity, high manufacturing costs, and high operating losses. Furthermore, it necessitates the use of isolation transformers for electrical isolation, further increasing the device's size, weight, and additional losses. To overcome the shortcomings of full-power solutions, the industry has gradually explored partial-capacity flexible power flow transfer devices. However, existing partial-capacity solutions still rely on isolation transformers; the series side still requires an isolation transformer to couple the output voltage to the grid. Although this solution reduces the number of isolation transformers, transformers still exist.

[0004] In summary, both traditional full-power back-to-back structures and existing partial-capacity series-parallel coupled structures suffer from drawbacks such as "reliance on isolation transformers leading to high costs, large size, and high losses" or "large capacity and numerous power devices reducing economic efficiency." These limitations make it difficult to fully meet the technical requirements of distribution networks for flexible power flow transfer devices in the context of high-proportion renewable energy integration. Therefore, developing a medium-voltage flexible power flow transfer device that eliminates the need for isolation transformers and balances economic efficiency and high performance has become an important direction for solving the current power flow optimization problem in distribution networks and promoting the consumption of renewable energy. Summary of the Invention

[0005] This invention proposes a low-cost, capacitor-coupled, medium-voltage flexible power flow conversion device and control method, belonging to the field of flexible power flow conversion technology for distribution networks. Each phase circuit of the device includes a three-arm power module, parallel port filter inductors and series port filter inductors and capacitors, and a medium-voltage capacitor bank. The reactive current of the medium-voltage capacitor is coupled with the output voltage of the first and second arms of the three-arm parallel port to maintain DC bus stability. Power flow regulation is achieved through the control of the second and third arms of the series port. To fully utilize the converter capacity, an adaptive segmented switching method for the capacitor bank is proposed. While maintaining DC voltage stability, this method keeps the modulation ratio of the parallel ports in a high range, thereby reducing the current withstand stress on the devices. This invention features no isolation transformer, compact structure, low cost, and small parallel branch current. Compared to traditional UPFC circuits, the power device capacity is further reduced, improving system economy.

[0006] The objective of this invention is achieved through the following technical solution: A low-cost, capacitively coupled medium-voltage flexible power transfer device and its control method, characterized in that it includes: measuring the voltage of the medium-voltage power grid 1 on the input side of the device using the voltage sensor according to claim 1. DC capacitor voltage of each phase 2. Voltage of medium-voltage power grid on the output side of the device According to claim 1, the current sensor measures the current at the parallel port. and series port current ； The controller measures the corresponding voltage signal based on the voltage sensor and the corresponding current signal based on the current sensor, and receives power flow transfer references from the power grid dispatch center. The controller includes a parallel port control module, a series port control module, a switching capacitor bank (TSC) control module, and a three-arm SVPWM vector modulation module. The parallel port control module receives the DC voltage of each phase. The power reference of each phase parallel port is obtained by controlling the DC voltage of each phase; the current amplitude of each phase in the parallel port is obtained by the phase-locked loop. and the phase of each phase current The modulation wave generation process generates modulation waves for each phase parallel port. The parallel port control module obtains the maximum value of each phase modulation wave through a maximum value selection step. Then calculate the maximum modulation ratio of the parallel ports. Phase it with the A-phase current Send to the capacitor bank switching control module; The capacitor bank switching control module receives the phase of phase A current. Triggered at phase angles of 0° and 180°, the maximum modulation ratio is discretized by a zero-order hold (ZOH) with a period of 10ms. The current switching command is obtained through the switching command determination stage. This allows us to obtain the number of medium-voltage capacitor banks that should currently be put into operation. N (k) And limit its amplitude; The capacitor bank switching control module will control the current number of capacitor banks. N (k) The signal is sent to the SCR switch signal determination stage to obtain the signal from the capacitor bank. SCR 1. SCR 2. SCR 3. Switch signal; The voltage of the power grid 2 on the output side of the serial port control module acquisition device is obtained. and the output current of the series port The active power supplied is obtained through power calculation. ; The series port control module collects the voltage of power grid 1. The phase reference of the series port is obtained through the phase-locked loop. And receive the active power reference issued by the dispatch center. The reference value of the series port current amplitude is obtained through the power control loop. The series port current reference is obtained through the dq / abc coordinate transformation process. By superimposing the voltage difference between grid 1 and grid 2 through the current controller, the series port modulated wave voltage is obtained. ; The controller receives the parallel port modulation voltage. and series port modulation voltage Then, the switching signals of each switching transistor in the three-bridge-arm circuit are obtained through the three-bridge-arm SVPWM vector modulation module.

[0007] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: 1. By applying the technical solution proposed in this invention, the isolation transformer can be eliminated, which can significantly reduce the size of the device and greatly reduce the hardware cost. It can also eliminate the copper and iron losses generated during the operation of the isolation transformer, effectively improving the overall operating efficiency of the device. 2. By applying the technical solution proposed in this invention, the parallel branch current during stable operation of the device can be significantly reduced, and the current withstand rating requirements of the power devices in the parallel branch can be greatly reduced. Compared with the traditional UPFC circuit, the capacity of the power devices can be further reduced, thus improving the system economy. 3. The device circuit structure proposed in this invention can avoid common-mode circulating current between series ports and parallel ports, and avoid the system protection problem caused by excessive common-mode circulating current in traditional back-to-back UPFC circuits, thereby improving equipment safety. 4. The non-isolated partial capacity flexible interconnection device and its control method proposed in this invention support flexible splicing and expansion in both hardware topology and control strategy, which can adapt to distribution network application scenarios of different voltage levels and greatly improve the device's scenario adaptability and application flexibility. Attached Figure Description

[0008] Figure 1 A three-phase electrical connection structure diagram of a capacitor-coupled low-cost medium-voltage flexible power transfer device and control method provided in an embodiment of the present invention; Figure 2 A flowchart illustrating the algorithm steps of a capacitively coupled, low-cost, medium-voltage flexible power transfer device and control method provided in this embodiment of the invention. Figure 3 A schematic diagram of the single-phase structure and controller of the low-cost medium-voltage flexible power transfer device provided in this embodiment of the invention; Figure 4 This is a detailed control block diagram of each control module of the low-cost medium-voltage flexible power transfer device provided in the embodiments of the present invention; Figure 5 A detailed block diagram of the intermediate voltage switching capacitor bank (TSC) control module provided in the embodiment of the present invention; Figure 6 These are the power curves of the flexible power transfer device under various operating conditions provided in the embodiments of the present invention. Figure 7 These are the voltage, current, and switching signal curves of the flexible power transfer device provided in this embodiment of the invention under various operating conditions; Figure 8 These are simulation details of the switching process of the flexible power flow transfer device under various operating conditions provided in the embodiments of the present invention; Figure 9 This is a schematic diagram of a module of an embodiment of a capacitively coupled low-cost medium-voltage flexible power transfer device and control method provided by the present invention; Figure 10 This is a schematic diagram of a low-cost, medium-voltage flexible power transfer device with capacitive coupling provided in an embodiment of the present invention. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The specific operational methods in the method embodiments can also be applied to the device embodiments or system embodiments. 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 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.

[0010] The present invention proposes a low-cost, capacitively coupled medium-voltage flexible power transfer device and control method, comprising the following steps: Please refer to Figure 1 for the electrical connection structure of a capacitor-coupled low-cost medium-voltage flexible power transfer device, characterized in that it includes: a medium-voltage power grid 1, a parallel bridge arm, an intermediate shared bridge arm, a parallel port filter inductor, a bidirectional thyristor, a switched capacitor bank, a DC capacitor, a series bridge arm, a series port filter inductor, a series port filter capacitor, a line impedance, a medium-voltage power grid 2, a current sensor, a voltage sensor, and a controller. The first voltage sensor is connected to the medium-voltage power grid 1 to measure the voltage of the medium-voltage power grid 1 on the input side of the device. The other end of the voltage sensor is connected to the midpoint of the intermediate shared bridge arm. One end of the parallel port filter inductor is connected to the midpoint of the parallel bridge arm through the first current sensor, and the other end is connected to the medium-voltage capacitor bank through a bidirectional thyristor. The capacitor bank is divided into three groups. The first group contains four capacitors and is connected to the medium-voltage capacitor bank through a bidirectional thyristor. SCR 1. Connection, the second group contains 2 capacitors and is connected via... SCR 2 connections, the third group contains 1 capacitor and is connected through SCR There are 3 connections, a total of 7 capacitors, and the capacitance of each capacitor is [value missing]. C0. The switching of the capacitor bank is achieved by turning on and off the bidirectional thyristor. One end of the series port filter inductor is connected to the middle of the series bridge arm, and the other end is connected to one end of the series capacitor through a second current sensor. The other end of the series capacitor is connected to the midpoint of the middle shared bridge arm. The parallel bridge arm, the middle shared bridge arm, and the series bridge arm are all connected in parallel across the DC capacitor. The second voltage sensor is installed across the DC capacitor. The third voltage sensor is installed at the output port of the device.

[0011] Please refer to Figure 2, which illustrates a capacitively coupled, low-cost, medium-voltage flexible power transfer device and its control method, including:

[0012] Step S201: According to the voltage sensor of claim 1, measure the voltage of the medium-voltage power grid 1 on the input side of the device. DC capacitor voltage of each phase 2. Voltage of medium-voltage power grid on the output side of the device According to claim 1, the current sensor measures the current at the parallel port. and series port current ； Please refer to Figures 3 and 4 for the specific control block diagrams of each control module of the low-cost medium-voltage flexible power transfer device provided in this embodiment of the invention, including: Step S202: The controller measures the corresponding voltage signal based on the voltage sensor and the corresponding current signal based on the current sensor, and receives power flow transfer reference from the power grid dispatch center. The controller includes a parallel port control module, a series port control module, a switching capacitor bank (TSC) control module, and a three-arm SVPWM vector modulation module; Step S203: The parallel port control module receives the DC voltage of each phase. The power reference for each phase parallel port is obtained by controlling the DC voltage of each phase, as shown in the following formula: (1) in, It is a DC voltage controller. and These are the proportional and integral coefficients of the controller, respectively. DC voltage reference; The sum of these values ​​is used to obtain the current amplitude of each phase at the parallel port through a phase-locked loop. and the phase of each phase current The modulation wave amplitude and instantaneous value are obtained through the modulation wave generation stage, as shown in the following formula: (2) in, For the amplitude of the modulated wave at the parallel port, The instantaneous value of the modulated wave at the parallel port; The parallel port control module obtains the maximum value of each phase modulation wave through a maximum value selection step. Then calculate the maximum modulation ratio of the parallel ports. As shown in the following formula: (3) The max function takes the maximum value among the amplitude values ​​of the three-phase modulation wave abc and sets it in phase with the phase A current. The signal is sent to the capacitor bank switching control module.

[0013] Please refer to Figure 5, which shows a detailed block diagram of the medium-voltage switching capacitor bank (TSC) control module in the device provided in this embodiment of the invention, including:

[0014] Step S204: The capacitor bank switching control module receives the phase of phase A current. Triggered at phase angles of 0° and 180°, the maximum modulation ratio is discretized by a zero-order hold (ZOH) with a period of 10ms. The capacitor switching command for the current k-th cycle is obtained through the switching command determination step. As shown in the following formula: (4) Then, the number of capacitor banks in the (k-1)th period of the previous period is added. The number of medium-voltage capacitor banks put into operation in the current k-th cycle is obtained. N (k) And limit its amplitude as shown in the following formula: (5) in, The initial capacitor bank is typically 1. This is the capacitor switching command for the k-th cycle; The capacitor bank switching control module will control the current number of capacitor banks. N (k) The signal is sent to the SCR switch signal determination stage to obtain the signal from the capacitor bank. SCR 1. SCR 2. SCR The switching signal for 3 is shown in the following formula: (6) in,[ SCR 1. SCR 2. SCR 3] These represent the switching signals of the three thyristors in the capacitor bank, respectively. N (k) This represents the number of capacitor banks that should be put into operation in the current k-th cycle.

[0015] Step S205: The series port control module device receives the output side grid 2 voltage collected by the sensor. and the output current of the series port The voltage and current components along the αβ axis are obtained through coordinate transformation, and the active power output of the device is obtained through power calculation. and reactive power As shown in the following formula: (7) in This is the filter cutoff frequency. , , , The output voltage and series port output current components of the device under the α and β axes are respectively identified. Step S206: The series port control module receives the grid voltage 1 collected by the sensor. The phase reference of the series port is obtained through the phase-locked loop. Receive active power reference data from the dispatch center. and no-reactive reference The reference value of the series port current amplitude is obtained through the power control loop. The series port current reference is obtained through the dq / abc coordinate transformation process. As shown in the following formula: (8) in, For the dq / abc coordinate transformation step, The phase reference of the power grid obtained by phase-locking, For active power controller, and These are the proportional and integral coefficients of the active power flow control loop. For reactive power controller, and These are the proportional and integral coefficients of the reactive power control loop; The series port control module uses the voltage difference between grid 1 and grid 2 as a voltage feedforward, and obtains the series port modulation voltage reference through the current controller. As shown in the following formula: (9) in, This is the reference current for the series port. and These are the proportional coefficient and resonant coefficient of the current controller, respectively. For controller bandwidth, This is the reference frequency.

[0016] Step S207: The controller obtains the parallel port modulation voltage. and series port modulation voltage Then, the switching signals of each switching transistor in the three-arm series-parallel circuit are obtained through the three-arm SVPWM vector modulation module.

[0017] Figure 6 shows the simulation operation effect of the medium-voltage flexible power transfer device under all operating conditions provided in the embodiment of the present invention. Figure 6(a) is a list of system operating conditions: Condition 1: No power transfer command received; Condition 2: Power transfer command received: 1.0MW active power and 0MVar reactive power; Condition 3: Power transfer command received: 2.0MW active power and 0MVar reactive power; Condition 4: Power transfer command received: 3.0MW active power and 0MVar reactive power.

[0018] Figure 6(b) shows the active and reactive power curves of the line transmission and the parallel branch under all operating conditions. It can be seen that in operating condition 1, since no power is received for power transfer, both active and reactive power transmission remain at 0. However, the parallel port needs to charge the DC bus, so all capacitors are engaged, resulting in 4.2 MVar of reactive power and 0 active power. When switching to operating condition 2 in 1.0 seconds, the active power transmission responds rapidly to 1.0 MW, with a response time of only 200 ms. Only one parallel capacitor is engaged, providing 0 MW of active power. At 2.0s, the system switches to operating condition 3, where the active power continues to increase to 2.0MW, while the reactive power of the line remains unchanged. The number of capacitors increases to 3, and the reactive power input is 2.1MVar. At 3.0s, the system switches to operating condition 4, where the active power continues to increase to 3.0MW. The response time remains around 200ms. Under all operating conditions, the transmitted reactive power and the active power of the parallel branches remain near 0MVar, verifying the feasibility of the proposed medium-voltage flexible power flow transfer device and control method.

[0019] Figure 7(a) shows the voltage of grid 2, line transmission current, and parallel branch current curves from top to bottom. It can be seen that as the power transfer reference increases, the amplitude of the line transmission current increases accordingly, as does the number of capacitor banks in the parallel branches, and the amplitude of the reactive current on the parallel side also increases. It is worth noting that there is a short-term resonance in the parallel branch current during capacitor switching. Figure 7(b) shows the maximum modulation ratio of the parallel port and the thyristor switching signal curves under all operating conditions. It can be seen that as the power transfer reference increases, the maximum value of the modulation ratio of the parallel port can be well maintained within the ideal range of 0.6~0.8, effectively ensuring the current stress of the three-arm power devices.

[0020] Figure 8 shows a simulation detail of the switching process of the flexible power transfer device under various operating conditions provided in the embodiment of the present invention. Figure 8(a) shows the switching process curve between operating condition 1 and operating condition 2, and Figure 8(b) shows the switching process curve between operating condition 2 and operating condition 3. It can be seen that when the reference power transfer is doubled, the voltage of the capacitor bank and the voltage of the series port are not affected by the switching process. At the same time, the voltage of the parallel port increases by 0.2kA, which is the reactive current provided by the capacitor bank. Figure 8(c) shows the switching process curve between operating condition 3 and operating condition 4. It can be seen that as the number of capacitors increases, the current of the parallel port gradually increases, but it is only 1 / 3 of that of the series bridge arm. This effectively illustrates that the capacitor-coupled low-cost medium-voltage flexible power transfer device and control method proposed in this example can effectively reduce the stress of power devices and significantly reduce the cost of the device.

[0021] 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.

[0022] 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.

[0023] The embodiment module is shown in Figure 9. A capacitively coupled, low-cost medium-voltage flexible power transfer device and control method include: The first acquisition module 901 measures the voltage signals of each phase according to the voltage sensor and measures the current signals of each phase according to the current sensor. The second acquisition module 902 obtains the reference value of the series port power of the medium-voltage flexible power flow transfer device according to the power flow transfer instruction issued by the power grid dispatch center. The first determining module 903 obtains the power reference of each phase parallel port according to the DC voltage control, obtains the three-phase modulation wave voltage of the parallel port through the parallel port modulation wave generation link, and determines the largest modulation wave amplitude in each phase according to the modulation wave amplitude comparison link, thereby determining the maximum modulation ratio. The second determining module 904 determines the capacitor switching command to be switched according to the capacitor switching command determining step, thereby obtaining the number of capacitor groups to be switched, and obtains the switching signals of each thyristor of the medium voltage capacitor group through the SCR switching command determining step. The third acquisition module 905 calculates the active and reactive power values ​​transferred by the current device based on the power calculation. The fourth acquisition module 906 obtains the series port current amplitude reference based on the power control loop, obtains the series port current reference through the coordinate transformation link, and then obtains the series port modulated wave voltage through the current controller. The fifth acquisition module 907 obtains the switching signals of each switching transistor in the three-arm series-parallel circuit according to the three-arm SVPWM vector modulation module.

[0024] Figure 10 is a schematic diagram of a capacitively coupled, low-cost, medium-voltage flexible power transfer device and control method provided in an embodiment of the present invention.

[0025] A schematic diagram of the medium-voltage flexible power supply device is shown in Figure 10. It includes a power conversion circuit 1001, a controller 1002, a memory 1003, and a computer program 1004 stored in the memory 1003 and executable on the controller 1002. When the controller 1002 executes the computer program 1004, it implements the steps in the above-described resonance suppression method embodiment, for example... Figure 2 The steps S201 to S207 are shown. Alternatively, when the controller 1002 executes the computer program 1004, it implements the functions of the above embodiments, such as the modules 901 to 907 shown in Figure 8.

[0026] For example, the computer program 1004 can be divided into one or more modules / units, which are stored in the memory 1003 and executed by the controller 1002 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 1004 in the reactive power and harmonics hybrid compensation system device. For example, the computer program 1004 can be divided into a first obtaining module, a second obtaining module, a first determining module, a second determining module, a third obtaining module, a fourth obtaining module, and a fifth obtaining module, with the functions of each module as follows: The first obtaining module measures the voltage signals of each phase based on the voltage sensor and measures the current signals of each phase based on the current sensor. The second acquisition module obtains the reference value of the series port power of the medium-voltage flexible power flow transfer device according to the power flow transfer instruction issued by the power grid dispatch center. The first determining module obtains the power reference of each phase parallel port based on DC voltage control, obtains the three-phase modulation wave voltage of the parallel port through the parallel port modulation wave generation stage, and determines the largest modulation wave amplitude in each phase based on the modulation wave amplitude comparison stage, thereby determining the maximum modulation ratio. The second determining module determines the capacitor switching command to be switched based on the capacitor switching command determining step, thereby obtaining the number of capacitor banks to be switched, and obtains the switching signals of each thyristor of the medium voltage capacitor bank through the SCR switching command determining step. The third acquisition module calculates the active and reactive power values ​​transferred by the current device based on the power calculation. The fourth module obtains the series port current amplitude reference based on the power control loop, obtains the series port current reference through the coordinate transformation stage, and then obtains the series port modulated wave voltage through the current controller. The fifth acquisition module obtains the switching signals of each switching transistor in the three-arm series-parallel circuit based on the three-arm SVPWM vector modulation module.

[0027] The described capacitively coupled low-cost medium-voltage flexible power transfer device and control method may include, but are not limited to, a power converter 1001, a controller 1002, and a memory 1003. Those skilled in the art will understand that Figure 9 is merely an example of a capacitively coupled low-cost medium-voltage flexible power transfer device and does not constitute a limitation on the medium-voltage flexible power transfer device. It may include more or fewer components than shown, or combine certain components, or use different components. For example, the power transformer life assessment terminal equipment may also include input / output devices, network access devices, buses, etc.

[0028] The controller 1002 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. The general-purpose processor may be a microprocessor or any conventional processor.

[0029] The memory 1003 can be an internal storage unit of the hybrid transformer device with energy storage system, or an external storage circuit of the hybrid transformer device with energy storage system. Examples include plug-in hard drives, smart media cards (SMC), secure digital cards (SD), and flash cards equipped on the hybrid transformer device. Furthermore, the memory 1003 can include both internal storage units and external storage devices of the hybrid compensation system device. The memory 1003 is used to store the computer program and other programs and data required by the hybrid transformer device with energy storage system. The memory 1003 can also be used to temporarily store data that has been output or will be output.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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. An electrical connection structure of a low-cost medium-voltage flexible power flow transfer device of a capacitive coupling type, characterized by, Comprise: Medium voltage grid 1, parallel bridge arm, intermediate shared bridge arm, parallel port filter inductance, bidirectional thyristor, switched capacitor bank, DC capacitor, series bridge arm, series port filter inductance, series port filter capacitor, line impedance, medium voltage grid 2, current sensor, voltage sensor and controller; The first voltage sensor is connected to the medium voltage power grid 1 for measuring the voltage of the device input side medium voltage power grid 1, the other end of the voltage sensor is connected to the intermediate shared bridge arm midpoint, one end of the parallel port filter inductance is connected to the parallel bridge arm midpoint through the first current sensor, the other end is connected to the medium voltage capacitor bank through the bidirectional thyristor, the capacitor bank is divided into three groups, the first group contains four capacitors and is connected through SCR 1, the second group contains two capacitors and is connected through SCR 2, and the third group contains one capacitor and is connected through SCR 3, a total of seven capacitors, and the capacity of a single capacitor is C 0, and the switching of the capacitor bank is realized by opening and closing the bidirectional thyristor. One end of the series port filter inductance is connected to the series bridge arm midpoint, and the other end is connected to one end of the series capacitor through the second current sensor, and the other end of the series capacitor is connected to the intermediate shared bridge arm midpoint, and the parallel bridge arm, the intermediate shared bridge arm and the series bridge arm are all connected in parallel to the two ends of the DC capacitor, and the second voltage sensor is installed at the two ends of the DC capacitor. The third voltage sensor is installed at the device output port.

2. A low-cost medium-voltage flexible power flow transfer device of a capacitive coupling type and a control method, characterized by, Comprise: The voltage sensor according to claim 1, measuring the device input side medium voltage network 1 voltage , the phase-to-phase DC capacitor voltage , the device output side medium voltage network 2 voltage , The current sensor of claim 1, measuring the shunt port current and the series port current ； The controller measures the corresponding voltage signal according to the voltage sensor, measures the corresponding current signal according to the current sensor, and accepts the power flow transfer reference issued by the grid dispatching center. The controller comprises a parallel port control module, a series port control module, a switched capacitor bank (TSC) control module, and a three-bridge arm SVPWM vector modulation module; The parallel port control module receives each phase DC voltage , obtains each phase parallel port power reference through each phase DC voltage control, obtains each phase current amplitude and each phase current phase through a phase-locked loop , and obtains each phase parallel port modulation wave through the modulation wave generating link. The parallel port control module obtains the maximum value of each phase modulation wave through a maximum selection link , and further calculates the maximum value of the parallel port modulation ratio , compares it with the phase of the A-phase current , and sends it to the switching capacitor group control module; The switching capacitor group control module receives A-phase current phase , and the current switching instruction is determined by a switching instruction determining element , and the number of medium-voltage capacitor groups that should be put into operation currently is obtained N (k) , and the number is limited The switching capacitor group control module determines the current capacitor group number N (k) The determined capacitor group number is sent to the SCR switching signal determination link, and then the switching signal of the capacitor group is obtained SCR 1、 SCR 2、 SCR 3 The series port control module collects the voltage of the device output side power grid 2 and the series port output current , and calculates the transferred active power by power calculation ; The series port control module collects grid 1 voltage , obtains series port phase reference through the phase-locked loop , and receives active reference issued by the dispatch center , obtains series port current amplitude reference through the power control loop , obtains series port current reference through the dq / abc coordinate transformation link , and obtains series port modulation wave voltage through the current controller by superimposing the grid 1 and grid 2 voltage difference ; The controller obtains a parallel port modulation voltage and a series port modulation voltage After that, the three-bridge-arm SVPWM vector modulation module is used to obtain the switching signals of the switching tubes of the three-bridge-arm circuit. 3.The capacitor-coupled low-cost medium-voltage flexible power flow transfer device and control method according to claim 2, characterized in that: The controller measures the corresponding voltage signal according to the voltage sensor, measures the corresponding current signal according to the current sensor, and accepts the power flow transfer reference issued by the grid dispatching center. The controller comprises a parallel port control module, a switched capacitor (TSC) control module, a series port control module, and a three-bridge arm SVPWM vector modulation module.

4. The low-cost, medium-voltage, flexible, and capacitive-coupled power flow transfer device and control method of claim 2, wherein: The parallel port control module receives each phase DC voltage Each phase parallel port power reference is obtained by each phase DC voltage control as shown in the following equation: (1) wherein, is a direct current voltage controller, and are proportional and integral coefficients of the controller, respectively, is a direct current voltage reference; the sum of the amplitudes of the phase currents of the parallel port, obtained by means of a phase-locked loop and the phases of the phase currents the amplitude and the instantaneous value of the modulation wave, obtained by means of the modulation wave generation block, as follows: (2) wherein, is the parallel port modulation amplitude, is the parallel port modulation instantaneous value; The parallel port control module obtains the maximum value of each phase modulation wave through a maximum selection link and further calculates the maximum value of the parallel port modulation ratio as shown in the following formula: (3) Wherein, the max function is to take the maximum value of the three-phase modulation wave amplitude of abc, and compare it with the phase of A-phase current is sent to the switching capacitor group control module.

5. The low-cost, medium-voltage, flexible, and capacitive-coupled power flow transfer device and control method of claim 2, wherein: The switching capacitor group control module receives the A-phase current phase Triggered at phase angle 0° and 180°, the modulation ratio maximum value is discretized by a zero-order holder (ZOH), the period is 10 ms, and the capacitor switching instruction of the current k period is obtained through a switching instruction determination link As shown in the following formula: (4) Then, the capacitor group number of the previous k-1 period is superimposed to obtain the capacitor group number of the current k period put into operation N (k) , and is limited, as shown in the following formula: (5) wherein, is the initial input capacitor bank, typically 1, is the capacitor switching command for the kth cycle; The switching capacitor group control module determines the current capacitor group number N (k) to the SCR switch signal determination link, and then obtains the switch signal of the capacitor group SCR 1、 SCR 2、 SCR 3, as shown in the following formula: (6) wherein, SCR 1、 SCR 2、 SCR 3] represent the switching signals of the three thyristors of the capacitor bank, respectively, N (k) the number of capacitor banks to be put into for the current kth cycle.

6. The low-cost, medium-voltage, flexible, and capacitive-coupled power flow transfer device and control method of claim 2, wherein: The series port control module device receives the output side power grid 2 voltage collected by the sensor , and series port output current , obtains voltage and current components under αβ axis through coordinate transformation, and obtains active power and reactive power of device output through power calculation and as shown in the following formula: (7) wherein is the filter cut-off frequency, , , , are the device output side voltage and series port output current components under the αβ-axes, respectively; The series port control module receives the voltage of power grid 1 collected by the sensor. The phase reference of the series port is obtained through the phase-locked loop. Receive active power reference data from the dispatch center. and no-reactive reference The reference value of the series port current amplitude is obtained through the power control loop. The series port current reference is obtained through the dq / abc coordinate transformation process. As shown in the following formula: (8) wherein, is the dq / abc coordinate transformation block, is the phase-locked grid 1 phase reference, is the active power controller, and are the proportional and integral coefficients of the active power flow control loop, is the reactive power controller, and are the proportional and integral coefficients of the reactive power control loop. The series port control module takes the voltage difference between the power grid 1 and the power grid 2 as a voltage feedforward, and obtains a series port modulation voltage reference through the current controller As shown in the following formula: (9) wherein, is a reference current for the series port, and are a proportional coefficient and a resonant coefficient of the current controller, respectively, is a controller bandwidth, is a reference frequency.

7. The low-cost, medium-voltage, flexible, and capacitive-coupled power flow transfer device and control method of claim 2, wherein: The controller obtains a parallel port modulation voltage and a series port modulation voltage After that, the three-bridge-arm SVPWM vector modulation module is used to obtain the switching signals of the switching tubes of the three-bridge-arm series-parallel circuit.

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