AC power transmission and distribution flexible interconnection method and device

Abstract

The invention discloses an AC power transmission and distribution flexible interconnection method and device. The method comprises the following steps: inputting a first power transmission and distribution voltage of a first transmission and distribution line into a first winding through a first AC port; the transformer unit transforms the first power transmission and distribution voltage to the second winding and the third winding to obtain a second winding voltage and a third winding voltage, and the second alternating current port superposes the second winding voltage and the alternating current voltage of the second current transformation unit to obtain a second power transmission and distribution voltage which is transmitted to the second transmission and distribution line. Electric energy interaction with the second conversion unit is completed through the first conversion unit. Power exchange between different transmission lines is controlled through the second conversion unit, and reactive power of different transmission and distribution lines is respectively controlled through the first conversion unit and the second conversion unit. And a series-parallel connection structure with more windings and more variable current units is expanded, so that flexible interconnection and power interaction among high-voltage level or multiple transmission and distribution lines are realized.

Description

Technical Field

[0001] This invention relates to the field of AC power transmission and distribution, and more particularly to a method and apparatus for flexible interconnection of AC power transmission and distribution. Background Technology

[0002] Flexible interconnection of AC power transmission and distribution mainly connects different power transmission and distribution lines through power electronic equipment, thereby realizing bidirectional flow and flexible control of active and reactive power between different power transmission and distribution lines and even different local power transmission and distribution networks. This further achieves the goals of seamless power transfer, optimizing power flow distribution, improving distribution network stability and flexibility, improving power quality (harmonic and unbalanced voltage compensation), and achieving fault isolation.

[0003] Existing AC flexible interconnection is mainly achieved through back-to-back connections of AC / DC converters. Specifically, an AC / DC converter consists of two converter units: one converts AC to DC, and the other converts DC back to AC. In a back-to-back connection, these two converter units are connected face-to-face, with power transmission occurring through a DC link. The capacity of power electronic converters is twice that of back-to-back interconnection. Furthermore, interconnection of transmission and distribution lines at medium and high voltage levels requires modular series technology, which increases the complexity of flexible interconnection technology and leads to high overall equipment costs and engineering costs. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method and device for flexible interconnection of AC power transmission and distribution, which can significantly reduce the required power electronic equipment capacity, reduce equipment costs, engineering complexity and engineering costs, and improve the efficiency and reliability of flexible interconnection of AC power transmission and distribution.

[0005] In a first aspect, embodiments of the present invention provide a flexible interconnection method for AC power transmission and distribution, applied to a flexible interconnection system for AC power transmission and distribution, used to achieve flexible interconnection and power interaction between two or more transmission and distribution lines of different or the same voltage levels. The AC power transmission and distribution flexible interconnection system includes a hybrid transformer composed of a transformer unit and a converter unit. The hybrid transformer includes a first AC side and a second AC side. The first AC side is connected to a first transmission and distribution line through a first AC port, and the second AC side is connected to a second transmission and distribution line through a second AC port. The first AC side is composed of a first winding of a transformer unit, and the second AC side is composed of a second winding of a transformer unit and a second converter unit connected in series. The DC side of the second converter unit is connected to an energy storage unit or the DC side of the first converter unit to complete power interaction. The first converter unit is connected to a third winding of the transformer unit. The AC power transmission and distribution flexible interconnection method includes: The first transmission and distribution voltage of the first transmission and distribution line is input into the first winding through the first AC port; After the first transmission voltage is transformed to the second winding and the third winding through the first winding, the second winding voltage and the third winding voltage are obtained respectively. The third winding voltage represents the AC voltage of the first converter unit. The second transmission and distribution voltage, obtained by superimposing the second winding voltage and the second converter unit AC voltage, is transmitted to the second transmission and distribution line through the second AC port. The power interaction between the first and second transmission and distribution lines is controlled by the second converter unit. The reactive power of the first and second transmission and distribution lines is controlled by the first and second converter units, respectively. The AC windings of other transformer units and the series connection structure of the converter units are connected to other transmission and distribution lines to realize the flexible interconnection of three or more transmission and distribution lines.

[0006] In some optional embodiments, voltage matching is achieved through the coordinated regulation of the second winding and the second converter unit. The matching control relationship between the voltage of the second winding, the AC voltage of the second converter unit, and the voltage of the second AC port is as follows: ; in, The number of turns in the first winding. The number of turns in the second winding. Indicates the second transmission voltage. This represents the second transmission and distribution voltage phasor. Indicates the first transmission voltage. This represents the first transmission and distribution voltage phasor. This represents the AC voltage of the second converter unit. This represents the AC voltage phasor of the second converter unit. This indicates the voltage of the second winding. This represents the voltage phasor of the second winding; The method for achieving voltage matching through the coordinated regulation of the second winding and the second converter unit is as follows: the transformer tap position and corresponding voltage are adjusted according to the steady-state AC voltage operating point; the AC side voltage of the second converter unit is adjusted according to the dynamic AC voltage operating point; the steady-state AC operating point is selected based on the operating efficiency of the hybrid transformer and the voltage dynamic adjustment margin; the dynamic operating point is determined based on the dynamic change of the voltage difference between the first transmission and distribution voltage and the second winding voltage, while the second winding voltage is determined by the first transmission and distribution voltage and the winding turns ratio. n 2 / n 1. If the dynamic voltage change margin of the second converter unit is sufficient, that is, the second converter unit can withstand the required dynamic voltage change, then the transformer tap position is relatively fixed, or even no tap is needed.

[0007] In some optional embodiments, the first formula between the second winding voltage, the second converter unit voltage, and the second transmission voltage under steady-state operation is:

[0008] To ensure that the second converter unit remains within its allowable operating range despite fluctuations in the first or second transmission and distribution voltage, the voltage of the second winding is adjusted via an on-load tap changer according to a first limiting condition. This first limiting condition is:

[0009] The intermediate voltage within the range defined in the first limiting condition is selected as the rated voltage operating point of the transformer's second winding under different transmission and distribution line angle deviations. The rated voltage operating point of the second winding is substituted into the first formula to obtain the corresponding AC rated voltage operating point of the second converter unit, so that the second converter unit has sufficient margin when the transmission and distribution voltage fluctuates. These represent the maximum voltage rise and the maximum voltage drop during the voltage fluctuation process of the first transmission and distribution line, respectively. These represent the maximum voltage rise and maximum voltage drop during the voltage fluctuation process of the second transmission and distribution line. These are the minimum and maximum AC voltages for the second converter unit to operate, respectively. This represents the phase difference between the first and second transmission voltages; If both the first and second transmission and distribution lines experience a voltage surge or a voltage drop during operation, the voltage of the second winding can be adjusted via an on-load tap changer according to the second limiting condition, so that the second converter unit operates within the allowable operating range under voltage fluctuations. The second limiting condition is:

[0010] The intermediate voltage within the range defined in the second constraint is selected as the rated voltage operating point of the transformer's second winding under different transmission and distribution line angle deviations. The rated voltage operating point of the second winding is substituted into the first formula to obtain the corresponding AC rated voltage operating point of the second converter unit, so that the second converter unit has sufficient margin when the transmission and distribution voltage fluctuates.

[0011] In some optional embodiments, the method further includes: The power of the first transmission and distribution line and the second transmission and distribution line is controlled by the current or power of the first converter unit and the second converter unit. The reactive power compensation of the second transmission and distribution line is controlled by the second converter unit; The second converter unit controls the interactive active power between the first transmission and distribution line and the second transmission and distribution line. The reactive power compensation of the first and second transmission and distribution lines is controlled by the first converter unit and the second converter unit.

[0012] In some optional embodiments, the method further includes: The complex power input to the first and second transmission and distribution lines is:

[0013] ; in, This indicates the complex power of the second transmission and distribution line. This indicates the active power of the second transmission and distribution line. This indicates the reactive power of the second transmission and distribution line. The voltage phasor represents the second transmission voltage. This indicates the common track of the AC voltage phasor of the second converter unit. This indicates the common track of the AC voltage phasors of the first converter unit. This represents the voltage phasor of the second winding; This represents the complex power of the first transmission and distribution line. This represents the active power of the first transmission and distribution line. This represents the reactive power of the first transmission and distribution line. This represents the voltage phasor on the third winding. This indicates the voltage across the third winding; The currents of the first converter unit and the second converter unit are controlled according to the following formulas to achieve interactive active and reactive power compensation control between the first transmission and distribution line and the second transmission and distribution line: Thus we get: ; in, This represents the current phasor of the second converter unit. This indicates the common track of the current phasors in the second converter unit. This represents the current phasor of the first converter unit. This indicates the common track of the current phasors in the first converter unit. This indicates the common rail for the multiple power of the first transmission and distribution line. This indicates the common rail of the voltage phasor of the second winding. This indicates the common track of the AC voltage phasor of the second converter unit. This indicates the common rail of the voltage phasor of the second winding; Alternatively, by controlling the power of the first converter unit and the second converter unit, the interactive active power and reactive power compensation power control of the first transmission and distribution line and the second transmission and distribution line can be achieved: ; ; in, , This represents the active power of the first converter unit. This represents the active power of the second converter unit. This represents the reactive power of the first converter unit. This represents the reactive power of the second converter unit. This represents the voltage phasor of the first winding. This indicates the number of turns in the third winding.

[0014] In some optional embodiments, the control of reactive power compensation and interactive active power of the first and second transmission and distribution lines includes: The voltage phase difference between the second converter unit and the first transmission and distribution line is: ;in, This indicates the voltage phase difference between the second converter unit and the first transmission and distribution line; The voltage phase difference between the second converter unit and the second transmission and distribution line is: ,in, This represents the voltage phase difference between the first and second transmission and distribution lines. This indicates the voltage phase difference between the second converter unit and the second transmission and distribution line; The second converter unit leads the first and second transmission and distribution lines in phase by: ;in, This indicates the angle by which the current of the second converter unit leads the voltage. This indicates that the second converter unit is ahead of the phase of the first transmission and distribution line. This indicates that the second converter unit leads the second transmission and distribution line in phase. The active and reactive power flowing out of the second transmission and distribution line are:

[0015] The active power and reactive power flowing into the second winding are:

[0016] in, This indicates the active power of the second winding. This indicates the reactive power of the second winding; The active power and reactive power flowing into the first winding from the second winding and the third winding are: ; ;in, This indicates that the first converter unit is ahead of the first transmission and distribution line in phase. This indicates the active power of the first winding. This indicates the reactive power of the first winding. This indicates the active power of the third winding. This indicates the reactive power of the third winding; The combined power of the first and second transmission and distribution lines is: ; ;in, This indicates the angle by which the current of the first converter unit leads the voltage. This indicates that the first converter unit is ahead of the first transmission and distribution line in phase.

[0017] In some optional embodiments, the method further includes: Considering that the synchronous coordinates of the second converter unit are located at the AC voltage of the second converter unit, the complex power of the first transmission and distribution line and the second transmission and distribution line is:

[0018] in, This represents the D-axis voltage of the second winding. This represents the Q-axis voltage of the second winding. This represents the Q-axis current of the first converter unit. This represents the Q-axis current of the second converter unit. This represents the D-axis current of the second converter unit; The control relationship between the active and reactive power of the second transmission and distribution line, controlled by the D and Q axis currents of the second converter unit, is as follows: ; With the synchronous coordinate of the first converter unit positioned at the AC voltage of the first converter unit, the control relationship for controlling the reactive power of the first transmission and distribution line through the Q-axis current of the first converter unit is as follows: .

[0019] In some optional embodiments, the control of the dynamic voltage and steady-state voltage of the first and second transmission and distribution lines includes: When the amplitude and phase of the second transmission and distribution voltage change dynamically, the dynamic change value of the second transmission and distribution voltage can be dynamically compensated by adjusting the amplitude and phase of the AC voltage of the second converter unit. The voltage difference between the first transmission and distribution voltage and the second winding voltage can be directly measured by the following formula and sent to the AC voltage feedforward link of the second converter unit to achieve dynamic voltage compensation: ;in, This represents the voltage phasor of the second converter unit. The phasor represents the initial value of the second transmission and distribution voltage. The phasor represents the initial value of the voltage in the second converter unit. This represents the dynamic change phasor of the second transmission and distribution voltage; When the first transmission and distribution voltage changes dynamically, the dynamic change value of the second transmission and distribution voltage can be dynamically compensated by adjusting the AC voltage amplitude and phase of the second converter unit. The voltage difference between the first transmission and distribution voltage and the second winding can be directly measured and sent to the AC voltage feedforward link of the second converter unit to achieve voltage dynamic compensation. Alternatively, the voltage difference between the first transmission and distribution voltage or the third winding can be directly measured and sent to the AC voltage feedforward link of the first converter unit to achieve voltage dynamic compensation.

[0020] in, This represents the phasor of the initial value of the first transmission and distribution voltage. This represents the phasor of the dynamic change in the first transmission and distribution voltage. This represents the initial value phasor of the voltage of the first converter unit.

[0021] In some optional embodiments, the hybrid transformer employs single-phase converter units and single-phase transformer units to realize the interconnection and interactive power control of single-phase active AC systems; or employs three-phase converter units and three-phase transformer units to realize the interconnection, active power interaction and reactive power control of three-phase active AC systems. The transformer unit adopts an electrical isolation structure with independent multi-windings to achieve electrical isolation between interconnected AC systems; the transformer unit also adopts a non-electrical isolation structure with non-independent multi-windings, which includes an autotransformer structure with winding center taps to further reduce the interconnection cost and volume of active AC systems. Based on the hybrid transformer structure, a single AC / DC converter unit is expanded into a cascaded configuration of multiple AC / DC converter units, or a single AC / DC converter unit is expanded into multiple cascaded configurations including isolated DC / DC converter units and AC / DC converter units connected in series, for flexible interconnection, power interaction control, and dynamic voltage regulation of high-voltage transmission and distribution lines. The hybrid transformer structure is further expanded to include multiple connecting windings and multiple converter units, or, based on a single multi-winding power frequency transformer or multiple double-winding transformers in the hybrid transformer structure, it is expanded to a parallel configuration of multiple converter units, each connecting to multiple transmission and distribution lines, achieving flexible interconnection, active power interaction, reactive power control, and dynamic voltage regulation among multiple transmission and distribution lines. The AC side of each converter unit is connected in series with a second winding via a transformer, forming electrical isolation between the AC side of the converter unit and the transmission and distribution lines, and high / low voltage conversion, achieving flexible interconnection, active power interaction, reactive power control, and dynamic voltage regulation among medium-voltage or (and) high-voltage multiple transmission and distribution lines.

[0022] In a second aspect, embodiments of the present invention provide a computer device, the computer device including a processor, a memory, and a computer program stored in the memory and executable by the processor, wherein when the computer program is executed by the processor, it implements the steps of the above-described method.

[0023] Thirdly, embodiments of the present invention provide a computer-readable storage medium storing a processor-executable program, which, when executed by a processor, is used to perform the method described above.

[0024] The implementation of this invention provides the following beneficial effects: This invention provides a flexible interconnection method for AC power transmission and distribution, comprising: inputting a first transmission and distribution voltage of the first transmission and distribution line into the first winding through the first AC port; transforming the first transmission and distribution voltage to the second winding and the third winding through the first winding to obtain a second winding voltage and a third winding voltage; and transmitting a second transmission and distribution voltage obtained by superimposing the second winding voltage and the AC voltage of the second converter unit to the second transmission and distribution line through the second AC port. Power exchange with the second converter unit is completed through the first converter unit. Furthermore, the power exchange between the first and second transmission lines is controlled through the second converter unit, and the reactive power of the first and second transmission and distribution lines is controlled by the first and second converter units respectively. This method can be extended to series-parallel structures with more windings and more converter units to achieve flexible interconnection and power exchange between high-voltage levels or multiple transmission and distribution lines. Therefore, this application can significantly reduce the required power electronic equipment capacity, reduce equipment costs, engineering complexity and engineering costs, and improve the efficiency and reliability of flexible interconnection of AC power transmission and distribution. Attached Figure Description

[0025] Figure 1 is a schematic diagram of a single-phase circuit of a hybrid transformer in an implementation environment provided by an embodiment of the present invention, including: Figure 1(a) a hybrid transformer with a low potential converter unit connected to three independent windings, Figure 1(b) a hybrid transformer with a high potential converter unit connected to three independent windings, Figure 1(c) a hybrid transformer with a high potential converter unit connected to two independent windings, and Figure 1(d) a hybrid transformer with a high potential H-bridge converter unit connected to two independent windings. Figure 2 This is a flowchart of a flexible interconnection method for AC power transmission and distribution provided in an embodiment of the present invention; Figure 3(a) is a single-phase schematic diagram of the AC-DC converter units cascaded in series according to an embodiment of the present invention; Figure 3(b) is a single-phase schematic diagram of the AC / DC converter unit and the isolated DC-DC converter unit cascaded in series according to an embodiment of the present invention; Figure 3(c) is a single-phase schematic diagram of the combined application of a single AC / DC converter unit and an energy storage battery provided in an embodiment of the present invention; Figure 3(d) is a single-phase schematic diagram of the flexible interconnection scheme of three transmission and distribution lines provided in an embodiment of the present invention; Figure 3(e) is a single-phase schematic diagram of a non-isolated hybrid transformer for interconnection of high-voltage transmission and distribution lines, formed by cascaded converter units, provided in an embodiment of the present invention. Figure 3(f) is a single-phase schematic diagram of an isolated hybrid transformer provided in an embodiment of the present invention, which expands from two AC / DC converter units to multiple AC / DC converter units on the basis of a single multi-winding transformer for interconnection of multiple transmission and distribution lines; Figure 3(g) is a single-phase schematic diagram of an isolation-type hybrid transformer provided in an embodiment of the present invention, which expands from two AC / DC converter units to multiple AC / DC converter units and is connected in series with the second winding through a transformer for interconnection of medium and high voltage transmission and distribution lines with the same or different voltages. Figure 4 This is a schematic diagram of the coordinated AC voltage control of the transformer unit and converter unit of the hybrid transformer provided in an embodiment of the present invention; Figure 5 This is a control block diagram of a hybrid transformer provided in an embodiment of the present invention; Figure 6 This is a diagram illustrating the dynamic steady-state effect of power control of a hybrid transformer when the feeder phase difference is zero, provided by an embodiment of the present invention. Figure 7 This is a diagram illustrating the dynamic steady-state effect of power control of a hybrid transformer when the feeder phase difference is ten degrees, as provided in an embodiment of the present invention. Figure 8 This is a diagram illustrating the dynamic control effect of the first transmission and distribution voltage of the hybrid transformer when the feeder phase difference is five degrees, as provided in an embodiment of the present invention. Figure 9 This is a diagram illustrating the dynamic control effect of the second transmission and distribution voltage of the hybrid transformer when the feeder phase difference is five degrees, as provided in an embodiment of the present invention. Figure 10 This is a schematic block diagram of the structure of a computer device provided in an embodiment of the present invention. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0027] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0028] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0029] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0030] This invention provides a method and apparatus for flexible interconnection of AC power transmission and distribution, applied to a flexible interconnection system for AC power transmission and distribution. It enables flexible interconnection and power exchange between two or more transmission and distribution lines of different or the same voltage levels. The AC power transmission and distribution flexible interconnection system includes a hybrid transformer composed of a transformer unit and a converter unit. The hybrid transformer includes a first AC side and a second AC side. The first AC side is connected to a first transmission and distribution line via a first AC port, and the second AC side is connected to a second transmission and distribution line via a second AC port. The first AC side is composed of a first winding of the transformer unit, and the second AC side is composed of a second winding of the transformer unit and a second converter unit connected in series. The DC side of the second converter unit is connected to an energy storage unit or the DC side of the first converter unit to complete power exchange. The first converter unit is connected to a third winding of the transformer unit. The AC power transmission and distribution flexible interconnection method includes: inputting a first transmission and distribution voltage of the first transmission and distribution line into the first winding through the first AC port; transforming the first transmission and distribution voltage to the second and third windings through the first winding to obtain a second winding voltage and a third winding voltage, where the third winding voltage represents the AC voltage of the first converter unit; transmitting a second transmission and distribution voltage obtained by superimposing the second winding voltage and the second converter unit AC voltage to the second transmission and distribution line through the second AC port, and controlling the power interaction between the first and second transmission and distribution lines through the second converter unit; controlling the reactive power of the first and second transmission and distribution lines respectively through the first and second converter units; and connecting to other transmission and distribution lines through a series connection structure of other transformer unit AC windings and converter units to achieve flexible interconnection of three or more transmission and distribution lines. Therefore, this application can significantly reduce the required power electronic equipment capacity, reduce equipment costs, engineering complexity and engineering costs, and improve the efficiency and reliability of AC power transmission and distribution flexible interconnection.

[0031] First, an exemplary description of the implementation environment of the present invention will be provided. This example is not intended to limit the specific equipment structure, but rather to illustrate a specific implementation environment in which the technical solution of the present invention can be executed. Referring to Figure 1, which is a schematic diagram of the implementation environment of an embodiment of the present invention, the AC power transmission and distribution flexible interconnection system of this embodiment includes a hybrid transformer. The hybrid transformer includes a first AC side and a second AC side. The first AC side is connected to a first transmission and distribution line through a first AC port, and the second AC side is connected to a second transmission and distribution line through a second AC port. The first AC side is composed of a first winding of a transformer unit (i.e., the first winding of the transformer unit), and the second AC side is composed of a second winding of a transformer unit (i.e., the second winding of the transformer unit) and a second converter unit connected in series. The DC side of the second converter unit completes the power exchange through an energy storage unit or the first converter unit. The first converter unit is connected to the third winding of the transformer unit. The energy storage unit includes a DC energy storage device, and the specific energy storage device is not limited here.

[0032] The control method of the present invention will be further described below based on the implementation environment shown in Figure 1.

[0033] Reference Figure 2 , Figure 2 This is a flowchart of an AC power transmission and distribution flexible interconnection method provided by an embodiment of the present invention. The AC power transmission and distribution flexible interconnection method includes, but is not limited to, the following steps: S210, the first transmission and distribution voltage of the first transmission and distribution line is input into the first winding through the first AC port; S220, after the first transmission voltage is transformed to the second winding and the third winding through the first winding, the second winding voltage and the third winding voltage are obtained respectively. The third winding voltage represents the AC voltage of the second converter unit. S230, the second transmission and distribution voltage obtained by superimposing the second winding voltage and the second converter unit AC voltage is transmitted to the second transmission and distribution line through the second AC port, and the power interaction between the first transmission and distribution line and the second transmission and distribution line is controlled through the second converter unit, and the reactive power of the first transmission and distribution line and the second transmission and distribution line is controlled through the first converter unit and the second converter unit respectively. S240 is connected to other transmission and distribution lines through the series connection structure of other transformer unit AC windings and converter units, in order to realize flexible interconnection of three or more transmission and distribution lines.

[0034] It should be noted that, referring to Figure 1, , These are the AC ports of two AC transmission and distribution lines, y (the first line) and k (the second line). Lines y and k can be of the same or different voltage levels, but they share the same grid frequency, meaning they are in the same synchronous grid. For two adjacent transmission and distribution lines in the same synchronous grid, their AC frequencies are the same, and their phase differences are small. For example, the AC phase difference between two adjacent 110kV / 220kV substations is within 15 degrees. The AC phase difference between two adjacent 10kV distribution lines below the same 110kV / 220kV substation is even smaller, generally within 10 degrees. In this case, a hybrid transformer as shown in Figure 1 can be used to interconnect high, medium, and low voltage wiring, significantly reducing the required power electronic converter capacity, thereby lowering equipment costs, engineering complexity, and project cost, while improving efficiency and system reliability. The hybrid transformer in Figure 1 can be a three-phase structure, in which case both the converter unit and the transformer are three-phase; or it can be a single-phase structure, in which case both the converter unit and the transformer are single-phase. Hybrid transformers can even have complex multiphase structures. In Figure 1, the first and second converter units can be bidirectional AC-DC voltage source converter units, bidirectional AC-DC current source converter units, or AC-DC converter units formed by a combination of bidirectional AC-DC and DC-AC. When used in high-voltage scenarios, the first and second converter units can also be cascaded structures composed of low-voltage AC-DC converter modules and isolated DC-DC converter modules.

[0035] Figure 3(a) shows a cascaded structure of two AC-DC units connected in series; Figure 3(b) shows a cascaded structure of an AC-DC unit and an isolated DC-DC unit connected in series; Figure 3(c) shows a single AC-DC converter unit combined with an energy storage battery; and Figure 3(d) shows a flexible interconnection structure of three transmission and distribution lines. The transformer-side converter unit can be a two-level, three-level, or multi-level AC-DC converter unit, or a modular multi-level AC-DC converter unit. Figure 3(e) is a single-phase schematic diagram of a hybrid transformer formed by cascaded converter units for interconnecting high-voltage transmission and distribution lines, provided by an embodiment of the present invention. This application describes the method according to a non-cascaded structure. The operation and control method of the cascaded structure is similar to that of the non-cascaded structure, except that the AC voltage of the converter unit in the former is evenly distributed in the cascaded structure before corresponding control.

[0036] The AC rated voltage of the first and second converter units shown in Figure 1 The rated voltage of the second power transmission and distribution line If the required converter unit capacity is only 20% of that of the traditional back-to-back scheme, the equipment cost will be significantly reduced. Since only a portion of the interactive power passes through the power electronic converter, the interconnection efficiency will also be significantly improved. Two wirings in the same local power grid may have an AC phase difference greater than 15 degrees due to differences in the connection groups of their corresponding windings. In this case, the AC transformer in Figure 1 can use the corresponding connection group to compensate for the excessive phase difference caused by the differences in the connection groups of other transformers, thereby keeping its phase difference within a small range.

[0037] In some optional embodiments, voltage matching is achieved through the coordinated regulation of the second winding and the second converter unit. The matching control relationship between the voltage of the second winding, the AC voltage of the second converter unit, and the voltage of the second AC port is as follows: ; in, The number of turns in the first winding. The number of turns in the second winding. Indicates the second transmission voltage. This represents the second transmission and distribution voltage phasor. Indicates the first transmission voltage. This represents the first transmission and distribution voltage phasor. This represents the AC voltage of the second converter unit. This represents the AC voltage phasor of the second converter unit. This indicates the voltage of the second winding. This represents the voltage phasor of the second winding; The method for achieving voltage matching through the coordinated regulation of the second winding and the second converter unit is as follows: the transformer tap position and corresponding voltage are adjusted according to the steady-state AC voltage operating point; the AC side voltage of the second converter unit is adjusted according to the dynamic AC voltage operating point; the steady-state AC operating point is selected based on the operating efficiency of the hybrid transformer and the voltage dynamic adjustment margin; the dynamic operating point is determined based on the dynamic change of the voltage difference between the first transmission and distribution voltage and the second winding voltage, while the second winding voltage is determined by the first transmission and distribution voltage and the winding turns ratio. n 2 / n 1. If the dynamic voltage change margin of the second converter unit is sufficient, that is, the second converter unit can withstand the required dynamic voltage change, then the transformer tap position is relatively fixed, or even no tap is needed.

[0038] In some optional embodiments, the first formula between the second winding voltage, the second converter unit voltage, and the second transmission voltage under steady-state operation is:

[0039] To ensure that the second converter unit remains within its allowable operating range despite fluctuations in the first or second transmission and distribution voltage, the voltage of the second winding is adjusted via an on-load tap changer according to a first limiting condition. This first limiting condition is:

[0040] The intermediate voltage within the range defined in the first limiting condition is selected as the rated voltage operating point of the transformer's second winding under different transmission and distribution line angle deviations. The rated voltage operating point of the second winding is substituted into the first formula to obtain the corresponding AC rated voltage operating point of the second converter unit, so that the second converter unit has sufficient margin when the transmission and distribution voltage fluctuates. These represent the maximum voltage rise and the maximum voltage drop during the voltage fluctuation process of the first transmission and distribution line, respectively. These represent the maximum voltage rise and maximum voltage drop during the voltage fluctuation process of the second transmission and distribution line. These are the minimum and maximum AC voltages for the second converter unit to operate, respectively. This represents the phase difference between the first and second transmission voltages; If both the first and second transmission and distribution lines experience a voltage surge or a voltage drop during operation, the voltage of the second winding can be adjusted via an on-load tap changer according to the second limiting condition, so that the second converter unit operates within the allowable operating range under voltage fluctuations. The second limiting condition is:

[0041] The intermediate voltage within the range defined in the second constraint is selected as the rated voltage operating point of the transformer's second winding under different transmission and distribution line angle deviations. The rated voltage operating point of the second winding is substituted into the first formula to obtain the corresponding AC rated voltage operating point of the second converter unit, so that the second converter unit has sufficient margin when the transmission and distribution voltage fluctuates.

[0042] Specifically, the basic principle of AC voltage coordination control is: the transformer unit and the converter unit in the hybrid transformer are coordinated and controlled by AC voltage, so that the transformer unit and the converter unit can work within a safe and efficient voltage range, and the hybrid transformer can operate safely and efficiently.

[0043] From the hybrid transformer circuit topology in Figure 1, we can see that:

[0044] in , and The voltages are, in order, the voltage of the transmission and distribution line k, the voltage of the second winding, and the AC voltage of the second converter unit. The voltage of the second winding is mainly determined by the first transmission and distribution voltage and the tap position. ; in, The number of turns in the first winding. The number of turns in the second winding is determined by the tap position; therefore, once the tap position is determined, the AC voltage of the second converter unit is controlled according to the following formula:

[0045] Coordination method for stabilizing AC voltage: To ensure the safe and efficient operation of the second converter unit and the hybrid transformer, the AC voltage of the second converter unit can be kept near its rated operating point during steady-state operation. This can be achieved by adjusting the tap voltage of the second winding to maintain steady-state operation at the rated operating point of the second converter unit.

[0046] in, This represents the complex number of the unit voltage of the second AC unit. This represents the rated voltage of the second converter unit, and j represents the imaginary unit.

[0047] like Figure 4 As shown, assume the voltage k of the transmission and distribution line is... With zero phase, the maximum voltage phase difference between y and k in the transmission and distribution line is: That is, the maximum phase difference is Within this range, the steady-state operating point of the second converter unit is... Figure 4 The area marked with a red line, that is, the area marked with a red line. The vertex is the center of the circle. On an arc with a radius equal to 1. The specific location is determined by the phase difference. Therefore, the voltage of the second winding can be calculated as follows:

[0048] The formula for the turns ratio of the second winding is:

[0049] The position of the second winding connector is adjusted according to the turns ratio formula.

[0050] In some optional embodiments, when the first and second transmission voltages change dynamically, the dynamic changes of the first and second transmission voltages are compensated by the rapid dynamic response of the second converter unit, and the amplitude of the dynamic response compensation of the second converter unit is maximized when the phase difference between the first and second transmission voltages is zero. When the phase difference between the first and second transmission voltages is zero, if the first transmission voltage remains constant and the second transmission voltage dynamically changes to a first maximum value, then the AC voltage of the second converter unit is dynamically adjusted to a first maximum value. This first maximum value is equal to the rated voltage of the AC voltage of the second converter unit plus the dynamic change value of the second transmission voltage, which is the difference between the first maximum value and the steady-state rated voltage of the second transmission voltage. ;in, This represents the first maximum value of the second converter unit. This indicates the first maximum value of the second transmission and distribution voltage. Indicates the second transmission voltage; When the phase difference between the first and second transmission voltages is zero, and if the second transmission voltage remains unchanged, then the first transmission voltage reaches its first minimum value, and the AC voltage of the second converter unit reaches its second maximum value. ;in, This represents the second maximum value of the second converter unit. This represents the first minimum value of the first transmission and distribution voltage. When the phase difference between the first and second transmission voltages is zero, the first transmission voltage reaches its first minimum value, and the second transmission voltage reaches its first maximum value, the AC voltage of the second converter unit reaches its second maximum value. The formula for calculating the second maximum value is as follows:

[0051] Specifically, the coordination method for dynamic changes in AC voltage: when the transmission line voltage... , The voltage of the second converter unit changes dynamically according to the formula. Corresponding dynamic adjustments are made to maintain the dynamic stability of the hybrid transformer. When the phase difference... The value is zero, indicating that the AC voltage adjustment range of the second converter unit caused by the dynamic changes in the transmission and distribution line voltage is the largest.

[0052] When phase difference When the voltage equals zero, the voltage of transmission line y remains constant, while the voltage of transmission line k dynamically changes to its maximum value. The AC voltage of the second converter unit reaches its first maximum value:

[0053] When phase difference When the voltage equals zero, the voltage at k in the transmission and distribution line remains constant, while the voltage at y in the transmission and distribution line dynamically changes to its minimum value. The AC voltage of the second converter unit reaches its second maximum value:

[0054] When phase difference The voltage y in the transmission and distribution line dynamically changes to its minimum value, equal to zero. Meanwhile, the voltage of transmission and distribution line k dynamically changes to its maximum value. The AC voltage of the second converter unit reaches its second maximum value:

[0055] Considering the maximum range of dynamic voltage in the power grid Then the formula for calculating the second maximum value is:

[0056] When the upstream local power grids of transmission and distribution lines y and k are the same, their voltages are unlikely to change in opposite directions simultaneously. Furthermore, the probability of simultaneous dynamic reversal of the voltages of transmission and distribution lines y and k is relatively low. In this case, the maximum AC voltage of the second converter unit can be designed based on the larger of the first and second maximum values.

[0057] In some optional embodiments, controlling the power of the first and second transmission and distribution lines by the current or power of the first and second converter units includes: The power of the first transmission and distribution line and the second transmission and distribution line is controlled by the current or power of the first converter unit and the second converter unit. The reactive power compensation of the second transmission and distribution line is controlled by the second converter unit; The second converter unit controls the interactive active power between the first transmission and distribution line and the second transmission and distribution line. The reactive power compensation of the first and second transmission and distribution lines is controlled by the first converter unit and the second converter unit.

[0058] In some optional embodiments, the method further includes: The complex power input to the first and second transmission and distribution lines is:

[0059] ; in, This indicates the complex power of the second transmission and distribution line. This indicates the active power of the second transmission and distribution line. This indicates the reactive power of the second transmission and distribution line. The voltage phasor represents the second transmission voltage. This indicates the common track of the AC voltage phasor of the second converter unit. This indicates the common track of the AC voltage phasors of the first converter unit. This represents the voltage phasor of the second winding; This represents the complex power of the first transmission and distribution line. This represents the active power of the first transmission and distribution line. This represents the reactive power of the first transmission and distribution line. This represents the voltage phasor on the third winding. This indicates the voltage across the third winding; The currents of the first converter unit and the second converter unit are controlled according to the following formulas to achieve interactive active and reactive power compensation control between the first transmission and distribution line and the second transmission and distribution line: Thus we get: ; in, This represents the current phasor of the second converter unit. This indicates the common track of the current phasors in the second converter unit. This represents the current phasor of the first converter unit. This indicates the common track of the current phasors in the first converter unit. This indicates the common rail for the multiple power of the first transmission and distribution line. This indicates the common rail of the voltage phasor of the second winding. This indicates the common track of the AC voltage phasor of the second converter unit. This indicates the common rail of the voltage phasor of the second winding; Alternatively, by controlling the power of the first converter unit and the second converter unit, the interactive active power and reactive power compensation power control of the first transmission and distribution line and the second transmission and distribution line can be achieved: ; ; in, , This represents the active power of the first converter unit. This represents the active power of the second converter unit. This represents the reactive power of the first converter unit. This represents the reactive power of the second converter unit. This represents the voltage phasor of the first winding. This indicates the number of turns in the third winding.

[0060] Specifically, the basic principle of interactive active and reactive power control is as follows: Based on the aforementioned voltage coordination, power control of transmission and distribution lines y and k can be achieved through current / power control of the first and second converter units. The interactive active power between transmission and distribution lines y and k is mainly controlled by the second converter unit, while the reactive power compensation power of transmission and distribution lines y and k is controlled by the first and second converter units respectively. As shown in Figure 1, the complex power input to the hybrid transformer of transmission and distribution lines k and y is:

[0061]

[0062] The currents of the first and second converter units are controlled by the following formulas, respectively, to achieve interactive active and reactive power compensation control of transmission and distribution lines y and k: Thus we get: ; Neglecting hybrid transformer losses, we have .

[0063] The power of the first and second converter units can also be controlled according to the following formula, thereby realizing the interactive active and reactive power compensation control of transmission and distribution lines y and k:

[0064]

[0065] and These represent the active and reactive power flowing into the first and second converter units from the AC side, respectively.

[0066] Furthermore, the DC voltage is controlled by the D-axis current of the first converter unit, thereby enabling the DC voltage to... It stabilizes at the required value and achieves power balance between the first and second converter units.

[0067] In some optional embodiments, the control of reactive power compensation and interactive active power of the first and second transmission and distribution lines includes: The voltage phase difference between the second converter unit and the first transmission and distribution line is: ;in, This indicates the voltage phase difference between the second converter unit and the first transmission and distribution line; The voltage phase difference between the second converter unit and the second transmission and distribution line is: ,in, This represents the voltage phase difference between the first and second transmission and distribution lines. This indicates the voltage phase difference between the second converter unit and the second transmission and distribution line; The second converter unit leads the first and second transmission and distribution lines in phase by: ;in, This indicates the angle by which the current of the second converter unit leads the voltage. This indicates that the second converter unit is ahead of the phase of the first transmission and distribution line. This indicates that the second converter unit leads the second transmission and distribution line in phase. The active and reactive power flowing out of the second transmission and distribution line are:

[0068] The active power and reactive power flowing into the second winding are:

[0069] in, This indicates the active power of the second winding. This indicates the reactive power of the second winding; The active power and reactive power flowing into the first winding from the second winding and the third winding are: ; ;in, This indicates that the first converter unit is ahead of the first transmission and distribution line in phase. This indicates the active power of the first winding. This indicates the reactive power of the first winding. This indicates the active power of the third winding. This indicates the reactive power of the third winding; The combined power of the first and second transmission and distribution lines is: ; ;in, This indicates the angle by which the current of the first converter unit leads the voltage. This indicates that the first converter unit is ahead of the first transmission and distribution line in phase.

[0070] In some optional embodiments, the method further includes: Considering that the synchronous coordinates of the second converter unit are located at the AC voltage of the second converter unit, the complex power of the first transmission and distribution line and the second transmission and distribution line is:

[0071] in, This represents the D-axis voltage of the second winding. This represents the Q-axis voltage of the second winding. This represents the Q-axis current of the first converter unit. This represents the Q-axis current of the second converter unit. This represents the D-axis current of the second converter unit; The control relationship between the active and reactive power of the second transmission and distribution line, controlled by the D and Q axis currents of the second converter unit, is as follows: ; With the synchronous coordinate of the first converter unit positioned at the AC voltage of the first converter unit, the control relationship for controlling the reactive power of the first transmission and distribution line through the Q-axis current of the first converter unit is as follows: .

[0072] Specifically, the implementation of interactive active and reactive power control: the voltage phase difference between the second converter unit and the transmission and distribution line y is:

[0073] The phase difference between the second converter unit and the transmission line k is: .

[0074] The current-voltage lead angle of the second converter unit is: Then the phase of the current in the second converter unit leading the transmission and distribution lines y and k is:

[0075] Therefore, the active and reactive power flowing out from transmission and distribution line k are:

[0076] The active and reactive power flowing into the second winding are:

[0077] The active power and reactive power flowing into the first winding from the second and third windings are:

[0078]

[0079] The actual power flowing from the third winding into the first winding is the same as the actual power flowing from the DC bus to the third winding, which is also the actual power flowing from the second converter unit to the DC bus. The complex power of transmission and distribution lines k and y is:

[0080]

[0081] Furthermore, the active and reactive power control of the first and second transmission and distribution lines based on the converter unit can be further developed and applied to AC voltage control, virtual synchronization control, and dynamic AC frequency support of the first and second transmission and distribution lines.

[0082] Consider the synchronous coordinates of the second converter unit located at its AC voltage. We can obtain:

[0083]

[0084] The matrix formula can be obtained as follows:

[0085] Consider the synchronous coordinates of the first converter unit located at its AC voltage. The current formula for the first converter unit on the Q-axis can be obtained as follows:

[0086] Adjusting the D and Q axis currents of the second converter unit according to the matrix formula can achieve active and reactive power control of transmission and distribution line k, where active power is the interactive power between transmission and distribution lines y and k. Adjusting the Q axis current of the first converter unit according to the Q axis current formula can achieve reactive power control of transmission and distribution line y.

[0087] Furthermore, the active and reactive power control of the first and second transmission and distribution lines based on the converter unit can be further developed and applied to AC voltage control, virtual synchronization control, and dynamic AC frequency support of the first and second transmission and distribution lines.

[0088] In some optional embodiments, the control of the dynamic voltage and steady-state voltage of the first and second transmission and distribution lines includes: When the amplitude and phase of the second transmission and distribution voltage change dynamically, the dynamic change value of the second transmission and distribution voltage can be dynamically compensated by adjusting the amplitude and phase of the AC voltage of the second converter unit. The voltage difference between the first transmission and distribution voltage and the second winding voltage can be directly measured by the following formula and sent to the AC voltage feedforward link of the second converter unit to achieve dynamic voltage compensation: ;in, This represents the voltage phasor of the second converter unit. The phasor represents the initial value of the second transmission and distribution voltage. The phasor represents the initial value of the voltage in the second converter unit. This represents the dynamic change phasor of the second transmission and distribution voltage; When the first transmission and distribution voltage changes dynamically, the dynamic change value of the second transmission and distribution voltage can be dynamically compensated by adjusting the AC voltage amplitude and phase of the second converter unit. The voltage difference between the first transmission and distribution voltage and the second winding can be directly measured and sent to the AC voltage feedforward link of the second converter unit to achieve voltage dynamic compensation. Alternatively, the voltage difference between the first transmission and distribution voltage or the third winding can be directly measured and sent to the AC voltage feedforward link of the first converter unit to achieve voltage dynamic compensation.

[0089] in, This represents the phasor of the initial value of the first transmission and distribution voltage. This represents the phasor of the dynamic change in the first transmission and distribution voltage. This represents the initial value phasor of the voltage of the first converter unit.

[0090] Specifically, the basic principle of dynamic and steady-state voltage (dynamic voltage and steady-state voltage) control for transmission and distribution lines is as follows: Hybrid transformers can also achieve dynamic and steady-state voltage adjustment for interconnected transmission and distribution lines, especially when the short-circuit ratio of a certain transmission and distribution line is relatively high and the local power grid where the transmission and distribution line is located is relatively weak, the adjustment effect is better. Generally, the series connection formed by the second converter unit and the first winding is connected to the transmission and distribution line of the weak power grid, while the third winding is connected to the transmission and distribution line of the strong power grid.

[0091] If the voltage of transmission line y is stronger than that of transmission line k, or if their strengths are roughly equal, then the voltage change of transmission line k needs to be dynamically adjusted based on the original voltage. This can be achieved by dynamically adjusting the AC voltage of the second converter unit, thus:

[0092] This refers to the dynamic voltage that the transmission and distribution line k needs to increase.

[0093] If it is necessary to increase the steady-state voltage of transmission and distribution line k, the steady-state voltage of transmission and distribution line k can be adjusted by adjusting the tap position of the first winding. According to the voltage coordination of the first winding and the second converter unit described above, the dynamic and steady-state voltage adjustment of transmission and distribution line k can be achieved.

[0094] If the voltage of transmission and distribution line k is stronger than that of transmission and distribution line y, or if their strengths are roughly equal, then the voltage change of transmission and distribution line y needs to be dynamically adjusted based on the original voltage. This can be achieved by simultaneously and dynamically adjusting the AC voltages of the first and second converter units. The voltage of the second converter unit is adjusted using the following formula:

[0095] Meanwhile, the voltage of the first converter unit is adjusted according to the following formula:

[0096] The above voltage adjustment works well when the voltage of the transmission line being adjusted is much weaker than that of another transmission line. If the difference in voltage strength between the y and k values ​​of the transmission line is not significant, the adjustment effect will be poor, and the voltage cannot be adjusted to the target value in one go. In this case, the adjustment amount can be gradually increased according to the above principle until the voltage reaches the target value, thus achieving the required voltage adjustment.

[0097] During the aforementioned dynamic voltage adjustment process, when the current of the first converter unit and the second converter unit reaches the limit value, further adjustment is stopped, and the current is ensured to be within the allowable range.

[0098] In some alternative embodiments, a control block diagram can be established based on the above formula, such as... Figure 5 As shown, the subscripts abc represent the three-phase values ​​of the variable. Hybrid transformer control (HT control) is equipment-level control, obtained from the preceding analysis. Converter unit control is unit-level control, no different from the constant current control of a conventional voltage source converter.

[0099] In some alternative embodiments, the operation includes: First, dynamic power control verification was performed when the feeder phase difference was zero degrees, such as... Figure 6 As shown. At this time, the AC voltage of the first winding is maintained at 8.25kV, and the voltage of the first converter unit and the second converter unit is maintained at 1.75kV. The active power transmitted from feeder y to feeder k is controlled at 8MW before 0.5s, then adjusted to 4MW until 1.0s, and then restored to 8MW after 1s. The reactive power transmitted to feeders y and k is controlled at 0MW before 0.5s, then adjusted to 1MW until 1.0s, and then restored to 0MW after 1s. The transmitted active and reactive power are flexibly controlled as expected according to the target.

[0100] Secondly, dynamic power control verification was performed when the feeder phase difference was 10 degrees, such as... Figure 7 As shown. At this time, the AC voltage of winding 2 is adjusted to 9.63kV, and the voltage of converter units 1 and 2 is maintained at 1.75kV. The active power transmitted from feeder y to feeder k is controlled to 8MW before 0.5s, then adjusted to 2MW until 1.0s, and then restored to 8MW after 1s. The reactive power transmitted to feeders y and k is controlled to 0MW before 0.5s, then adjusted to 1.2MW until 1.0s, and then restored to 0MW after 1s. The transmitted active and reactive power are flexibly controlled as expected according to the target.

[0101] Secondly, dynamic verification of operation control was performed when the feeder phase difference was 10 degrees, such as... Figure 7As shown. At this time, the AC voltage of the first winding is adjusted to 9.63kV, and the voltage of the first converter unit and the second converter unit is maintained at 1.75kV. The active power transmitted from feeder y to feeder k is controlled at 8MW before 0.5s, then adjusted to 2MW until 1.0s, and then restored to 8MW after 1s. The reactive power transmitted to feeders y and k is controlled at 0MW before 0.5s, then adjusted to 1.2MW until 1.0s, and then restored to 0MW after 1s. The transmitted active and reactive power are flexibly controlled as expected according to the target.

[0102] Figure 8 The dynamic changes in AC voltage and its control response of transmission line k are shown when the phase difference is 5 degrees. The voltage dropped from 1 pu to 0.95 pu in 0.3 seconds, and then after 0.4 seconds... The voltage then recovered from 0.95 pu to 1.0 pu. Correspondingly, the AC voltage of the second converter unit dynamically decreased from 1750V to 1250V in 0.3 seconds, and then recovered to 1750V after 0.4 seconds; while the AC current of the second converter unit dynamically adjusted from 462A to 486A in 0.3 seconds, and then recovered to 462A after 0.4 seconds, thus maintaining the transmission power at approximately 8MW. Figure 8 It can be seen that although the interactive power between transmission and distribution lines generates dynamic power disturbances when the AC voltage of transmission and distribution line k changes, the overall interactive power between transmission and distribution lines y and k remains unchanged through hybrid transformer control.

[0103] Figure 9 shows the dynamic change of AC voltage and its control response in transmission and distribution line y when the phase difference is 5 degrees. The voltage dropped from 1 pu to 0.95 pu in 0.3 seconds, and then after 0.5 seconds... The voltage then recovers from 0.95 pu to 1.0 pu. Correspondingly, the AC voltage of the second converter unit increases from 1750V to 2250V in 0.3s, and then returns to 1750V after 0.5s, while the AC current of the second converter unit remains constant during this process. Because the AC voltage of the second converter unit increases while the AC current remains constant, the power transmitted from the second converter unit to transmission line k increases accordingly. Therefore, the AC current of the first converter unit increases from 486A to 618A, thus keeping the DC voltage constant. During this process, the AC voltage and AC current of transmission line k remain constant, thus maintaining the transmitted power at approximately 8MW. Figure 8 It can be seen that although the interactive power between transmission and distribution lines generates dynamic power disturbances when the AC voltage of transmission and distribution line y changes, the overall interactive power between transmission and distribution lines y and k remains unchanged through hybrid transformer control.

[0104] The first and second converter units of the hybrid transformer can be two-level, three-level, or multi-level AC-DC converter units, or modular multi-level AC-DC converter units. The above is introduced according to the non-cascaded structure. The operation and control method of the cascaded structure is similar to that of the non-cascaded structure, except that the AC voltage of the converter unit in the former is evenly distributed in the cascaded structure before corresponding control. The above-mentioned AC transmission and distribution flexible interconnection method can be used for both single-phase and three-phase circuits, and is mainly used for the flexible interconnection of three-phase transmission and distribution lines.

[0105] In some optional embodiments, the hybrid transformer employs single-phase converter units and single-phase transformer units to realize the interconnection and interactive power control of single-phase active AC systems; or employs three-phase converter units and three-phase transformer units to realize the interconnection, active power interaction and reactive power control of three-phase active AC systems. The transformer unit adopts an electrical isolation structure with independent multi-windings to achieve electrical isolation between interconnected AC systems; the transformer unit also adopts a non-electrical isolation structure with non-independent multi-windings, which includes an autotransformer structure with winding center taps to further reduce the interconnection cost and volume of active AC systems. Based on the hybrid transformer structure, a single AC / DC converter unit is expanded into a cascaded configuration of multiple AC / DC converter units, or a single AC / DC converter unit is expanded into multiple cascaded configurations including isolated DC / DC converter units and AC / DC converter units connected in series, for flexible interconnection, power interaction control, and dynamic voltage regulation of high-voltage transmission and distribution lines. The hybrid transformer structure is further expanded to include multiple connecting windings and multiple converter units, or, based on a single multi-winding power frequency transformer or multiple double-winding transformers in the hybrid transformer structure, it is expanded to a parallel configuration of multiple converter units, each connecting to multiple transmission and distribution lines, achieving flexible interconnection, active power interaction, reactive power control, and dynamic voltage regulation among multiple transmission and distribution lines. The AC side of each converter unit is connected in series with a second winding via a transformer, forming electrical isolation between the AC side of the converter unit and the transmission and distribution lines, and high / low voltage conversion, achieving flexible interconnection, active power interaction, reactive power control, and dynamic voltage regulation among medium-voltage or (and) high-voltage multiple transmission and distribution lines.

[0106] The implementation of this invention provides the following beneficial effects: This invention provides a flexible interconnection method for AC power transmission and distribution, comprising: inputting a first transmission and distribution voltage of the first transmission and distribution line into the first winding through the first AC port; transforming the first transmission and distribution voltage to the second winding and the third winding through the first winding to obtain a second winding voltage and a third winding voltage, the third winding voltage representing the AC voltage of the first converter unit; and transmitting a second transmission and distribution voltage obtained by superimposing the second winding voltage and the second converter unit AC voltage to the second transmission and distribution line through the second AC port. Power exchange with the second converter unit is completed through the first converter unit. Furthermore, the power exchange between the first and second transmission lines is controlled through the second converter unit, and the reactive power of the first and second transmission and distribution lines is controlled by the first and second converter units respectively. This can be extended to series-parallel structures with more windings and more converter units to achieve flexible interconnection and power exchange between high-voltage levels or multiple transmission and distribution lines. Therefore, this application can significantly reduce the required power electronic equipment capacity, reduce equipment costs, engineering complexity and engineering costs, and improve the efficiency and reliability of flexible interconnection of AC power transmission and distribution.

[0107] Low cost: The cost is lower due to the hybrid structure combining a power frequency transformer and a mature AC / DC converter. Furthermore, the system cost is further reduced due to partial power handling functions, the reuse of the second converter unit, and coordination with the power system and protection systems.

[0108] High efficiency: Due to the relatively simple system structure, fewer conversion levels, application of some power processing functions, and utilization of efficient and mature technologies of power frequency transformers and AC / DC conversion units, the overall system efficiency is high.

[0109] Coordination with power systems and protection: Due to the use of power frequency transformers, it can be coordinated with traditional AC protection; in addition, it provides some additional functions, such as transformer-to-location and AC charging metering.

[0110] Flexible control and scalability: This device and method facilitate rapid and flexible coordinated control of energy storage and electric vehicle power, thereby significantly reducing the impact on the AC power grid and improving supercharging capabilities. Furthermore, its distributed structure allows for easy expansion and flexible combined applications.

[0111] like Figure 10As shown, in a second aspect, embodiments of the present invention also provide a computer device, which can be a terminal. The computer device includes a processor, a memory, and a network interface connected via a system bus. The memory may include a non-volatile storage medium and internal memory. The non-volatile storage medium may store an operating system and a computer program. The computer program includes program instructions, which, when executed, cause the processor to execute any industrial equipment visualization management method. The processor provides computing and control capabilities to support the operation of the entire computer device. The internal memory provides an environment for the execution of the computer program in the non-volatile storage medium; when executed by the processor, the computer program causes the processor to execute any industrial equipment visualization management method. The network interface is used for network communication, such as sending assigned tasks. Those skilled in the art will understand that... Figure 10 The structure shown is merely a block diagram of a portion of the structure related to the present disclosure and does not constitute a limitation on the computer equipment to which the present disclosure is applied. Specific computer equipment may include, for example, [the following is a list of possible additional structures]. Figure 10 The processor may have more or fewer components, or combine certain components, or have different component arrangements. It should be understood that the processor may be a Central Processing Unit (CPU), or it may be 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. In one embodiment, the processor is used to run a computer program stored in memory to perform the following steps: inputting a first transmission voltage of the first transmission line into the first winding through the first AC port; transforming the first transmission voltage through the first winding to the second winding and the third winding to obtain a second winding voltage and a third winding voltage, the third winding voltage representing the AC voltage of the first converter unit; and transmitting a second transmission voltage obtained by superimposing the second winding voltage and the second converter unit AC voltage to the second transmission line through the second AC port.

[0112] It is evident that the content of the above method embodiments is applicable to this device embodiment. The specific functions implemented in this device embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0113] Furthermore, this application also discloses a computer program product or computer program stored in a computer-readable storage medium. A processor of a computer device can read the computer program from the computer-readable storage medium, and the processor executes the computer program, causing the computer device to perform the described method. Similarly, the content of the above method embodiments is applicable to this storage medium embodiment. The specific functions implemented in this storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0114] It is understood that all or some of the steps and systems in the methods disclosed above can be implemented as software, firmware, hardware, or suitable combinations thereof. Some or all of the physical components can be implemented as processors, such as central processing units, digital information processors, or microprocessors executing software, or as hardware, or as integrated circuits, such as application-specific integrated circuits. Such software can be distributed on computer-readable media, which can include computer storage media (or non-transitory media) and communication media (or transient media). As is known to those skilled in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and is accessible to a computer. Furthermore, as is known to those skilled in the art, communication media typically contain computer-readable instructions, data structures, program modules, or other data in modulated data information such as carrier waves or other transmission mechanisms, and may include any information delivery medium.

[0115] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for flexible interconnection of AC power transmission and distribution, characterized in that, A flexible interconnection system for AC power transmission and distribution is used to achieve flexible interconnection and power exchange between two or more transmission and distribution lines of different or the same voltage level. The AC power transmission and distribution flexible interconnection system includes a hybrid transformer composed of a transformer unit and a converter unit. The hybrid transformer includes a first AC side and a second AC side. The first AC side is connected to a first transmission and distribution line through a first AC port, and the second AC side is connected to a second transmission and distribution line through a second AC port. The first AC side is composed of a first winding of a transformer unit, and the second AC side is composed of a second winding of a transformer unit and a second converter unit connected in series. The DC side of the second converter unit is connected to an energy storage unit or the DC side of the first converter unit to complete power exchange. The first converter unit is connected to the third winding of the transformer unit to realize flexible interconnection and power exchange between the two transmission and distribution lines. The AC power transmission and distribution flexible interconnection method includes: The first transmission and distribution voltage of the first transmission and distribution line is input into the first winding through the first AC port; After the first transmission voltage is transformed to the second winding and the third winding through the first winding, the second winding voltage and the third winding voltage are obtained respectively. The third winding voltage represents the AC voltage of the first converter unit. The second transmission and distribution voltage, obtained by superimposing the second winding voltage and the second converter unit AC voltage, is transmitted to the second transmission and distribution line through the second AC port. The active power interaction between the first and second transmission and distribution lines is controlled by the second converter unit. The reactive power of the first and second transmission and distribution lines is controlled by the first and second converter units, respectively. Other transmission and distribution lines are connected through the series connection structure of the AC windings of other transformer units and converter units to realize the flexible interconnection of three or more transmission and distribution lines.

2. The method according to claim 1, characterized in that, Voltage matching is achieved through the coordinated regulation of the second winding and the second converter unit. The matching control relationship between the voltage of the second winding, the AC voltage of the second converter unit, and the voltage of the second AC port is as follows: ； in, The number of turns in the first winding. The number of turns in the second winding. Indicates the second transmission voltage. This represents the second transmission and distribution voltage phasor. Indicates the first transmission voltage. This represents the first transmission and distribution voltage phasor. This represents the AC voltage of the second converter unit. This represents the AC voltage phasor of the second converter unit. This indicates the voltage of the second winding. This represents the voltage phasor of the second winding; The method for achieving voltage matching through the coordinated regulation of the second winding and the second converter unit is as follows: the transformer tap position and corresponding voltage are adjusted according to the steady-state AC voltage operating point; the AC side voltage of the second converter unit is adjusted according to the dynamic AC voltage operating point; the steady-state AC operating point is selected based on the operating efficiency of the hybrid transformer and the voltage dynamic adjustment margin; the dynamic operating point is determined based on the dynamic change of the voltage difference between the first transmission and distribution voltage and the second winding voltage, while the second winding voltage is determined by the first transmission and distribution voltage and the winding turns ratio. n 2 / n 1. If the dynamic voltage change margin of the second converter unit is sufficient, that is, the second converter unit can withstand the required dynamic voltage change, then the transformer tap position is relatively fixed, or even no tap is needed.

3. The method according to claim 2, characterized in that, Under steady-state operation, the first formula relating the voltage of the second winding, the voltage of the second converter unit, and the second transmission and distribution voltage is: To ensure that the second converter unit remains within its allowable operating range despite fluctuations in the first or second transmission and distribution voltage, the voltage of the second winding is adjusted via an on-load tap changer according to a first limiting condition. This first limiting condition is: The intermediate voltage within the range defined in the first limiting condition is selected as the rated voltage operating point of the transformer's second winding under different transmission and distribution line angle deviations. The rated voltage operating point of the second winding is substituted into the first formula to obtain the corresponding AC rated voltage operating point of the second converter unit, so that the second converter unit has sufficient margin when the transmission and distribution voltage fluctuates. These represent the maximum voltage rise and the maximum voltage drop during the voltage fluctuation process of the first transmission and distribution line, respectively. These represent the maximum voltage rise and maximum voltage drop during the voltage fluctuation process of the second transmission and distribution line. These are the minimum and maximum AC voltages for the second converter unit to operate, respectively. This represents the phase difference between the first and second transmission voltages; If both the first and second transmission and distribution lines experience a voltage surge or a voltage drop during operation, the voltage of the second winding can be adjusted via an on-load tap changer according to the second limiting condition, so that the second converter unit operates within the allowable operating range under voltage fluctuations. The second limiting condition is: The intermediate voltage within the range defined in the second constraint is selected as the rated voltage operating point of the transformer's second winding under different transmission and distribution line angle deviations. The rated voltage operating point of the second winding is substituted into the first formula to obtain the corresponding AC rated voltage operating point of the second converter unit, so that the second converter unit has sufficient margin when the transmission and distribution voltage fluctuates.

4. The method according to claim 1, characterized in that, Controlling the power of the first and second transmission and distribution lines by adjusting the current or power of the first and second converter units includes: The second converter unit controls the interactive active power between the first transmission and distribution line and the second transmission and distribution line. The reactive power compensation of the second transmission and distribution line is controlled by the second converter unit; The reactive power compensation of the first transmission and distribution line is controlled by the first converter unit.

5. The method according to claim 4, characterized in that, The method of controlling the power of the first transmission and distribution line and the second transmission and distribution line through the current or power of the first converter unit and the second converter unit includes: The complex power input to the first and second transmission and distribution lines is: ； in, This indicates the complex power of the second transmission and distribution line. This indicates the active power of the second transmission and distribution line. This indicates the reactive power of the second transmission and distribution line. The voltage phasor represents the second transmission voltage. This indicates the common track of the AC voltage phasor of the second converter unit. This indicates the common track of the AC voltage phasors of the first converter unit. This represents the voltage phasor of the second winding; This represents the complex power of the first transmission and distribution line. This represents the active power of the first transmission and distribution line. This represents the reactive power of the first transmission and distribution line. This represents the voltage phasor on the third winding. This indicates the voltage across the third winding; The currents of the first converter unit and the second converter unit are controlled according to the following formulas to achieve interactive active and reactive power compensation control between the first transmission and distribution line and the second transmission and distribution line: Thus we get: ； in, This represents the current phasor of the second converter unit. This indicates the common track of the current phasors in the second converter unit. This represents the current phasor of the first converter unit. This indicates the common track of the current phasors in the first converter unit. This indicates the common rail for the multiple power of the first transmission and distribution line. This indicates the common rail of the voltage phasor of the second winding. This indicates the common track of the AC voltage phasor of the second converter unit. This indicates the common rail of the voltage phasor of the second winding; Alternatively, by controlling the power of the first converter unit and the second converter unit, the interactive active power and reactive power compensation power control of the first transmission and distribution line and the second transmission and distribution line can be achieved: ； ； in, , This represents the active power of the first converter unit. This represents the active power of the second converter unit. This represents the reactive power of the first converter unit. This represents the reactive power of the second converter unit. This represents the voltage phasor of the first winding. This indicates the number of turns in the third winding.

6. The method according to claim 5, characterized in that, The control of reactive power compensation and interactive active power of the first and second transmission and distribution lines includes: The voltage phase difference between the second converter unit and the first transmission and distribution line is: ;in, This indicates the voltage phase difference between the second converter unit and the first transmission and distribution line; The voltage phase difference between the second converter unit and the second transmission and distribution line is: ,in, This represents the voltage phase difference between the first and second transmission and distribution lines. This indicates the voltage phase difference between the second converter unit and the second transmission and distribution line; The second converter unit leads the first and second transmission and distribution lines in phase by: ;in, This indicates the angle by which the current of the second converter unit leads the voltage. This indicates that the second converter unit is ahead of the phase of the first transmission and distribution line. This indicates that the second converter unit leads the second transmission and distribution line in phase. The active and reactive power flowing out of the second transmission and distribution line are: The active power and reactive power flowing into the second winding are: in, This indicates the active power of the second winding. This indicates the reactive power of the second winding; The active power and reactive power flowing into the first winding from the second winding and the third winding are: ； ;in, This indicates that the first converter unit is ahead of the first transmission and distribution line in phase. This indicates the active power of the first winding. This indicates the reactive power of the first winding. This indicates the active power of the third winding. This indicates the reactive power of the third winding; The combined power of the first and second transmission and distribution lines is: ； ;in, This indicates the angle by which the current of the first converter unit leads the voltage. This indicates that the first converter unit is ahead of the first transmission and distribution line in phase.

7. The method according to claim 6, characterized in that, The method further includes: With the synchronous coordinates of the second converter unit positioned at the AC voltage of the second converter unit, the complex power of the first transmission and distribution line and the second transmission and distribution line is: in, This represents the D-axis voltage of the second winding. This represents the Q-axis voltage of the second winding. This represents the Q-axis current of the first converter unit. This represents the Q-axis current of the second converter unit. This represents the D-axis current of the second converter unit; The control relationship between the active and reactive power of the second transmission and distribution line, controlled by the D and Q axis currents of the second converter unit, is as follows: ； With the synchronous coordinate of the first converter unit positioned at the AC voltage of the first converter unit, the control relationship for controlling the reactive power of the first transmission and distribution line through the Q-axis current of the first converter unit is as follows: 。 8. The method according to claim 1, characterized in that, The control of dynamic and steady-state voltages of the first and second transmission and distribution lines includes: When the amplitude and phase of the second transmission and distribution voltage change dynamically, the dynamic change value of the second transmission and distribution voltage can be dynamically compensated by adjusting the amplitude and phase of the AC voltage of the second converter unit. The voltage difference between the first transmission and distribution voltage and the second winding voltage can be directly measured by the following formula and sent to the AC voltage feedforward link of the second converter unit to achieve dynamic voltage compensation: ;in, This represents the voltage phasor of the second converter unit. The phasor represents the initial value of the second transmission and distribution voltage. The phasor represents the initial value of the voltage in the second converter unit. This represents the dynamic change phasor of the second transmission and distribution voltage; When the first transmission and distribution voltage changes dynamically, the dynamic change value of the second transmission and distribution voltage can be dynamically compensated by adjusting the AC voltage amplitude and phase of the second converter unit. The voltage difference between the first transmission and distribution voltage and the second winding can be directly measured and sent to the AC voltage feedforward link of the second converter unit to achieve voltage dynamic compensation. Alternatively, the voltage difference between the first transmission and distribution voltage or the third winding can be directly measured and sent to the AC voltage feedforward link of the first converter unit to achieve voltage dynamic compensation. in, This represents the phasor of the initial value of the first transmission and distribution voltage. This represents the phasor of the dynamic change in the first transmission and distribution voltage. This represents the initial value phasor of the voltage of the first converter unit.

9. The method according to claim 1, characterized in that, The hybrid transformer employs single-phase converter units and single-phase transformer units to realize the interconnection and interactive power control of single-phase active AC systems; the hybrid transformer employs three-phase converter units and three-phase transformer units to realize the interconnection, active power interaction, and reactive power control of three-phase active AC systems. The transformer unit adopts an electrical isolation structure with independent multi-windings to achieve electrical isolation between interconnected AC systems; the transformer unit also adopts a non-electrical isolation structure with non-independent multi-windings, which includes an autotransformer structure with winding center taps to further reduce the interconnection cost and volume of active AC systems. Based on the hybrid transformer structure, a single AC / DC converter unit is expanded into a cascaded configuration of multiple AC / DC converter units, or a single AC / DC converter unit is expanded into multiple cascaded configurations including isolated DC / DC converter units and AC / DC converter units connected in series, for flexible interconnection, power interaction control, and dynamic voltage regulation of high-voltage transmission and distribution lines. The hybrid transformer structure is further expanded to include multiple connecting windings and multiple converter units, or, based on a single multi-winding power frequency transformer or multiple double-winding transformers in the hybrid transformer structure, it is expanded to a parallel configuration of multiple converter units, each connecting to multiple transmission and distribution lines, achieving flexible interconnection, active power interaction, reactive power control, and dynamic voltage regulation among multiple transmission and distribution lines. The AC side of each converter unit is connected in series with a second winding via a transformer, forming electrical isolation between the AC side of the converter unit and the transmission and distribution lines, and high / low voltage conversion, achieving flexible interconnection, active power interaction, reactive power control, and dynamic voltage regulation among medium-voltage or (and) high-voltage multiple transmission and distribution lines.

10. A computer device, wherein, The computer device includes a processor, a memory, and a computer program stored in the memory and executable by the processor, wherein the computer program, when executed by the processor, implements the method as described in any one of claims 1-9.

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