Smart transformer connected between different distribution lines to control power flow and distribution system control system employing the same

Abstract

The present invention discloses a smart transformer connected between different distribution lines to control power flow and a distribution system control system employing the same, which enables stable power supply by controlling power flow between different distribution lines in a distribution system that supplies power from a substation of a transmission system to a consumer.

Description

Technology Field

[0001] The present invention relates to a smart transformer connected between different distribution lines to control power flow and a distribution system control system employing the same, and more specifically, to a technology capable of supplying stable power by controlling power flow between different distribution lines in a distribution system that supplies power from a substation of a transmission system to a consumer. Background Technology

[0003] The configuration of the power distribution system can be classified into three types, such as radial, loop, and network types, as shown in Fig. 1.

[0004] Power supply reliability increases in the order of radial, loop, and network methods, but facility utilization may decrease. For example, loop and network methods have the advantage of high reliability as power can be supplied through other lines in the event of a fault. However, since other lines must handle the capacity of the faulty line in the event of a fault, the normal operating capacity is reduced, which has the disadvantage of lower facility utilization.

[0005] Although all three of the above line systems can be applied to domestic extra-high voltage (22.9kV) distribution lines, a unidirectional radial structure is adopted.

[0006] The current distribution sector of the domestic power system is responding to increased electricity demand solely through the quantitative expansion of transmission lines. While this quantitative response in the distribution system may be the most economical solution for the current increase in power demand, considering not only the increase in demand but also the numerous large-capacity renewable energy facilities expected to be integrated into the distribution system, relying solely on quantitative expansion through simple line additions has limitations in maintaining power quality.

[0007] For example, existing distribution networks utilized unidirectional distribution lines designed solely to supply power to consumers, eliminating the need to consider bidirectional current. However, due to the increasing volume of renewable energy connections, generation in some regions has exceeded load, resulting in reverse current flowing toward substations. When reverse current occurs in a unidirectionally designed system, it necessitates consideration of numerous factors from a distribution operation perspective, such as changes to protection coordination methods in the event of a system fault.

[0008] Furthermore, in the case of existing distribution systems, since there are no power facilities capable of current control within the system, the increase in renewable energy generation leads to reverse current phenomena, causing problems that require the installation of bidirectional protective relays and the revision of line operation processes.

[0009] Furthermore, since there are no power flow control facilities applicable to the current AC distribution system, simple interconnection at terminals or intermediate points poses a risk of generating circulating current or distribution line overloads. In order to resolve the reverse current phenomenon increasing at the distribution end due to the expansion of renewable energy, and to eliminate circulating current and overloads while maintaining a stable AC distribution voltage, an economical power flow control facility is required to control the phase of the voltage at the substation output end. Prior art literature

[0011] Korean Patent Registration No. 10-1132759, Korean Patent Publication No. 10-2018-0010026, Korean Patent Publication No. 10-2019-0124450 The problem to be solved

[0012] The present invention has been devised to solve the problems of the prior art as described above, and aims to provide a smart transformer capable of controlling the power flow of two different distribution lines without changing the currently established distribution system or revising the operation process.

[0013] In particular, this aims to resolve the problem of reverse current occurring towards the substation as the amount of renewable energy generated exceeds the load due to the construction of new and renewable energy generation facilities, which necessitates the installation of bidirectional protective relays to control the reverse current phenomenon or the revision of the line operation process itself.

[0014] Furthermore, we aim to solve the problem of not being able to stably provide distribution voltage due to the occurrence of circulating current or distribution line overload when simply connecting at the end or intermediate point, caused by the absence of power flow control equipment applicable to the current AC distribution system.

[0015] The objectives of the present invention are not limited to those foregoing, and other objectives and advantages of the present invention not mentioned may be understood from the following description. means of solving the problem

[0017] To solve the above problem, an embodiment of a smart transformer according to the present invention that controls power flow by connecting between different distribution lines may include: a multi-winding transformer in which the number of input terminals and the number of output terminals are adjusted, wherein the first distribution line is connected to a primary winding to which the first distribution line is connected; a secondary winding including a main winding and an additional winding that are separated into two lines, wherein the second distribution line is connected to the main winding and a power converter is connected to the additional winding; and a power converter having one end connected to the output terminal of the additional winding of the secondary winding and the other end connected to the output terminal of the main winding of the secondary winding to control power flow between the first distribution line and the second distribution line.

[0018] For example, the first distribution line and the second distribution line supply three-phase power, and the main transformer section is characterized by including a primary winding connected to the first distribution line; and a secondary winding including a main winding and an additional winding configured to be separated into two wires for each phase of the three-phase power, so that power flow can be controlled by connecting between different distribution lines.

[0019] Furthermore, the main transformer section can adjust the winding ratio of the primary winding and the secondary winding based on the difference between the voltage of the first distribution line and the voltage of the second distribution line.

[0020] Here, the primary winding of the main transformer section can be connected to the first distribution line in either a Y connection or a delta connection.

[0021] In addition, the main winding of the main transformer section is connected to the second distribution line in either a Y connection or a delta connection, and the additional winding of the main transformer section can be connected to the power converter in a delta connection.

[0022] Preferably, the power conversion unit may include: a rectifier, one side of which is connected to an additional winding of the secondary winding to convert AC to DC and receive active power required for power flow control from the additional winding to supply reactive power required for reactive power compensation; and an inverter, one side of which is connected to the other side of the rectifier and the other side of which is connected to the main winding of the secondary winding to convert DC to AC and adjust an injection voltage required for power flow control and a phase angle of the injection voltage.

[0023] Furthermore, the power conversion unit may further include a filter comprising an inductor with one end connected to the output terminal of the inverter; and a capacitor with one end connected to the other end of the inductor and the other end connected to the main winding of the secondary winding.

[0024] Going a step further, it may additionally include a switch unit that selectively connects the power converter to the main winding of the secondary winding according to the performance of the power flow function.

[0025] As an example, the power converter may further include a DC link capacitor disposed between the rectifier and the inverter, and the switch may include a first switch that selectively connects the filter to the main winding of the secondary winding; a second switch that selectively connects the neutral point of the DC link capacitor and the capacitor neutral point of the filter to the main winding of the secondary winding; and a switch controller that selectively operates the first switch and the second switch depending on whether power regulation is performed and whether a fault occurs in either the first distribution line or the second distribution line.

[0026] For example, it may further include a voltage compensator in which the primary winding is connected to the main winding of the main transformer section and the second distribution line, and the secondary winding is connected to the power converter section to provide a compensation voltage for each phase.

[0027] In addition, an embodiment of a power distribution system control system according to the present invention may include: a transmission system in which a power generation facility and a substation are connected in a mesh structure; a power distribution system comprising a plurality of distribution lines separated from each other to supply power to different consumers, configured as one or more stages after the substation; and the smart transformer connected between two different distribution line stages selected in the power distribution system to control the power flow of the distribution lines.

[0028] As an example, the two distribution lines to which the smart transformer is connected may be selected from among a plurality of distribution lines connected from a single main transformer facility located in a single substation.

[0029] As an example, the two distribution lines to which the smart transformer is connected may be selected from among a plurality of distribution lines each connected from different main transformer facilities located in a single substation.

[0030] As an example, the two distribution lines to which the smart transformer is connected may be selected from among a plurality of distribution lines connected from each main transformer facility located at different substations. Effects of the invention

[0032] According to the present invention, it is possible to control the power flow of two different distribution lines without changing the currently established distribution system or revising the operation process.

[0033] In particular, the present invention can provide an economical power flow control device for power distribution comprising a transformer with a multi-winding structure and a power converter with a small capacity relative to the transformer capacity. Furthermore, by combining a small-capacity power converter capable of active power control with a passive transformer that lacks control functions, power flow control that could not be performed with conventional transformers becomes possible.

[0034] Furthermore, since the present invention requires only a small-capacity power converter compared to the SOP method, power flow can be controlled economically. Because only one transformer is used, the structure is simpler than the UPFC method, the capacity of the power converter is smaller, and the constraints on the required installation space can be eliminated.

[0035] Going a step further, by applying the smart transformer according to the present invention, the first distribution line and the second distribution line can be electrically insulated, and the connection can be cut off so as not to affect other distribution lines in the event of an emergency on the distribution line, thereby ensuring the stability of system operation. In addition, since the turn ratio of the primary and secondary sides of the main transformer section can be adjusted, the present invention can be applied to different types of distribution lines with large voltage differences.

[0036] In addition, since the power flow of distribution lines can be controlled by applying the present invention to various types of distribution networks, the increasing amount of new and renewable energy can be economically accommodated without the need for additional expansion of distribution lines.

[0037] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description below. Brief explanation of the drawing

[0039] Figure 1 illustrates a conceptual diagram of the configuration of a power distribution system. FIG. 2 illustrates a configuration diagram of an embodiment of a smart transformer that controls power flow by connecting different distribution lines according to the present invention. FIG. 3 illustrates a circuit diagram of an embodiment of a smart transformer that controls power flow by connecting different distribution lines according to the present invention. FIG. 4 illustrates an embodiment of the main transformer section in a smart transformer connected between different power distribution lines according to the present invention to control power flow. FIG. 5 illustrates an embodiment of a power conversion unit in a smart transformer that controls power flow by connecting different power distribution lines according to the present invention. FIG. 6 illustrates a configuration diagram of another embodiment of a smart transformer connected between different power distribution lines to control power flow according to the present invention. FIG. 7 illustrates a circuit diagram of another embodiment of a smart transformer connected between different distribution lines according to the present invention to control power flow. FIG. 8 illustrates a configuration diagram of an embodiment of a power distribution system control system according to the present invention. Specific details for implementing the invention

[0040] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings, but the present invention is not limited or restricted by the embodiments.

[0041] In order to explain the present invention, the operational advantages of the present invention, and the objectives achieved by the implementation of the present invention, preferred embodiments of the present invention are illustrated below and examined with reference thereto.

[0042] First, the terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention; singular expressions may include plural expressions unless the context clearly indicates otherwise. Furthermore, in this application, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0043] In describing the present invention, if it is determined that a detailed description of related known components or functions may obscure the essence of the invention, such detailed description is omitted.

[0045] The present invention presents a smart transformer connected between different distribution lines of an existing distribution system to control power flow, and further presents a distribution system control system capable of controlling power flow to distribution lines of a distribution system by applying the smart transformer according to the present invention.

[0046] If active power facilities capable of controlling power flow according to system conditions exist within the distribution network, facility utilization rates can be increased, and consequently, renewable energy connection capacity can be expanded by utilizing existing lines and facilities.

[0047] Unlike distribution systems, transmission systems operate various active control facilities for system control. Reactive power compensation devices include SCVs and STATCOMs, while active power control devices include TCSCs and UPFCs.

[0048] Although it may be possible to apply UPFCs capable of controlling active and reactive power flow to distribution systems, applying UPFCs to distribution systems requires series / parallel inverters capable of handling the full power capacity required for UPFC compensation, requires installation space considering the size of the device, and incurs high costs for device construction, so it is not practically appropriate to apply UPFCs to distribution systems.

[0049] Furthermore, Soft Open Point (SOP) technology, utilizing a back-to-back voltage-type inverter structure, is capable of improving continuous power supply efficiency and reducing fault propagation during emergencies through distribution line interconnection technology, continuous current exchange between two distribution lines, and functions such as tripping and reactive power supply in emergencies. This SOP technology can potentially resolve the issue of reverse current increasing at the distribution level due to the expansion of renewable energy, while maintaining the protection system of the domestic unidirectional radial distribution line system. However, SOP technology faces challenges in actual grid application because constructing back-to-back inverters capable of handling the entire line capacity incurs significantly high costs, and securing a sufficiently large site for installation is also required.

[0050] Therefore, the present invention aims to present a power flow control technology for distribution that can resolve various problems arising from the actual application of the technologies described above to the power system, enables power flow control at an economical cost by being located between two busbars of the distribution line, and requires minimal installation space.

[0051] As an example, the present invention presents a smart transformer comprising a multi-winding transformer and a power conversion means having a small capacity relative to the transformer capacity, thereby economically controlling the power flow of distribution power and, through this, presenting a system capable of controlling the power flow of the entire distribution system.

[0052] In particular, the present invention presents a smart transformer capable of power flow control that could not be performed through conventional transformers by combining a small-capacity power converter capable of active power control with a passive transformer that lacks a control function.

[0053] The technology presented in this invention requires only a small-capacity power converter compared to the SOP method, so it can economically control the power flow of the wiring line. Furthermore, compared to the UPFC method, it has a simpler structure, requires less capacity for the power converter, and requires less installation space for the device, so it is a technology that can be immediately applied to the currently established power system.

[0054] We will examine the smart transformer according to the present invention through examples, and next, we will examine a power system control system capable of controlling the entire power system by employing the smart transformer according to the present invention through examples.

[0056] FIGS. 2 to 5 present an embodiment of a smart transformer connected between different power distribution lines according to the present invention to control power flow.

[0057] FIG. 2 illustrates a configuration diagram of an embodiment of a smart transformer connected between different distribution lines to control power flow according to the present invention, FIG. 3 illustrates a circuit diagram of an embodiment of a smart transformer according to the present invention, FIG. 4 illustrates an embodiment of a main transformer section in a smart transformer, and FIG. 5 illustrates an embodiment of a power conversion section in a smart transformer.

[0058] An embodiment of the smart transformer according to the present invention according to the present invention shown in FIGS. 2 to 5 will be explained with reference.

[0059] The smart transformer (100) presented in the present invention can be applied to both single-phase and three-phase power, and the following embodiments will be described as embodiments for three-phase power.

[0060] The smart transformer (100) may include a main transformer section (110), a power conversion section (130), a switch section (150), etc.

[0061] The main transformer section (110) may be a low-frequency main transformer (LFT) with a multi-winding structure. For example, the main transformer section (110) may be a multi-winding transformer with a controlled number of input terminals and output terminals, and may be composed of a primary winding (111), a secondary winding including a main winding (113) separated into two independent lines, and an additional winding (115).

[0062] The smart transformer (100) is connected between the first and second distribution lines, which are separated from each other and supply power to a consumer, and the primary winding (111) of the main transformer (110) is connected to the first distribution line (10), and the main winding (113) of the secondary winding can be connected to the second distribution line (50). Additionally, the additional winding (115) of the secondary winding can be connected to a power conversion unit (130) that controls power flow.

[0063] As seen in the above embodiment, when supplying three-phase power, the power of each phase R, S, and T of the first distribution line (10) is connected to the primary winding (111), and the secondary winding can be configured as a main winding (113) and an additional winding (115) by independently separating each of the R, S, and T phases of the three-phase power into two wires without internally connecting the connections of each of the three phases R, S, and T of the secondary winding. The power of each of the R, S, and T phases of the second distribution line (50) can be connected to the main winding (113), and the power of each of the R, S, and T phases of the additional winding (115) can be connected to the power conversion unit (130).

[0064] In the above embodiment, the primary winding (111) of the main transformer section (110) is connected to the first distribution line (10) in a delta connection manner, but depending on the situation, the primary winding (111) and the first distribution line (10) may be connected in a Y connection manner.

[0065] In addition, in the above embodiment, the main winding (113) of the secondary winding of the main transformer section (110) and the second distribution line (50) are connected in a Y-connection manner, but depending on the situation, the main winding (113) of the secondary winding and the second distribution line (50) may be connected in a delta connection manner. Similarly, the additional winding (115) of the secondary winding and the power conversion section (130) are connected in a delta connection manner, but a Y-connection method may also be applied.

[0066] Furthermore, the main transformer section (110) can adjust the winding ratio of the primary winding and the secondary winding based on the voltage difference between the first distribution line (10) and the second distribution line (50). That is, by adjusting the turn ratio of the primary winding and the secondary winding, it can be applied to heterogeneous wiring lines with a large voltage difference.

[0067] For example, the turns (N) of the primary winding and the secondary winding of the main transformer section (110) P / N s By designing by adjusting the ) power flow control is possible even between MV-class 22.9kV distribution and LV-class 380V distribution by applying the smart transformer (100) according to the present invention. Therefore, the smart transformer proposed in the present invention can be easily connected to any distribution line of 22.9kV or lower.

[0068] If the magnitude of the voltage of the connection where the main power is connected is the same, winding N P and N s is identical, and additional winding N AuxThe turn ratio can be determined by the maximum magnitude of the voltage injected for power flow control. For example, if Ns : NAux = 10 : 1, the voltage V of the additional winding (115) Aux is the voltage V of the main winding (113). TR It will have a size that is 1 / 10 of that of the others.

[0069] The power conversion unit (130) can regulate the power flow of two different distribution lines.

[0070] For example, the power conversion unit (130) may include a power conversion converter of 10% of the transformer capacity. Here, the capacity of the power conversion unit (130) may be changed according to the magnitude of the injection voltage to obtain the required power flow. That is, the smart transformer (100) according to the present invention may additionally construct a series transformer equal to the converter capacity of the power conversion unit (130) based on the required capacity.

[0071] One end of the power conversion unit (130) is connected to the output terminal of the additional winding (115) of the secondary winding, and the other end is connected to the output terminal of the main winding (113) of the secondary winding, so that the power flow of the first distribution line (10) and the second distribution line (50) can be controlled.

[0072] The power conversion unit (130) may be configured as a two-stage structure including a rectifier (131) that converts alternating current to direct current and an inverter (135) that converts direct current to alternating current.

[0073] The rectifier (131) can receive a three-phase AC voltage and generate a DC link voltage. The inverter (135) can generate a three-phase AC voltage using the DC link voltage generated by the rectifier (131). In the above embodiment, a three-phase circuit is described as an example, but it is not limited thereto, and a multi-level converter or other power conversion devices of various structures applicable to three-phase power conversion may be applied.

[0074] One side of the rectifier (131) is connected to an additional winding (115) of the secondary winding, and can convert alternating current into direct current, receive active power required for power flow control from the additional winding (115), and supply reactive power required for reactive power compensation.

[0075] One side of the inverter (135) is connected to the other side of the rectifier (131) and the other side is connected to the main winding (113) of the secondary winding to convert direct current into alternating current, and can adjust the injection voltage required for power flow control and the phase angle of said injection voltage. Here, the magnitude of the injection voltage can be determined by the DC link voltage and the modulation rate of the inverter.

[0076] In addition, the power conversion unit (130) may include a filter (137).

[0077] The filter (137) may include an inductor (138) with one side connected to the output terminal of the inverter (135) and a capacitor (139) with one side connected to the other side of the inductor (138) and the other side connected to the main winding (113) of the secondary winding.

[0078] The main winding (113) of the secondary winding of the main transformer section (110) can be completed in a Y-connection through the Y-connection of the capacitor (139) included in the filter (137).

[0079] Through this configuration, the three-phase output voltage and phase of the inverter (135) can be controlled, thereby enabling control of the power flow to the three-phase power of the distribution line.

[0080] Furthermore, the power conversion unit (130) may further include a DC link capacitor (133) placed between the rectifier (131) and the inverter (135).

[0081] The neutral point of the DC capacitor (133) and the neutral point of the capacitor (139) of the filter (137) can be connected to each other. Phase imbalance in the output of the inverter (135) can be resolved through the DC link capacitor (133).

[0082] In addition to the neutral point connection method presented in the above embodiment, various methods for phase imbalance control may be applied, such as a 4-leg inverter topology.

[0083] The switch unit (150) can selectively connect the power converter unit (130) to the main winding (113) of the secondary winding depending on the performance of the power flow function.

[0084] The switch unit (150) may include a first switch (151) that selectively connects the filter (137) of the power conversion unit (130) to the main winding (113) of the secondary winding, and a second switch (155) that selectively connects the neutral point of the DC link capacitor (133) and the capacitor neutral point (139) of the filter (137) to the main winding (113) of the secondary winding.

[0085] And the switch unit (150) may include a switch controller (not shown) that selectively operates the first switch (151) and the second switch (155) depending on whether power coordination is performed and whether an accident occurs in either the first distribution line (10) or the second distribution line (50).

[0086] When the smart transformer (100) does not perform the power flow control function, the second switch (155) can be turned ON to perform the function of bypassing the grid voltage.

[0087] When the smart transformer (100) normally performs the power flow control function, the second switch (155) is turned OFF, and the capacitor (139) placed in the filter (137) of the power converter (130) is connected in series, so that the main winding (113) of the secondary winding is completed in a Y connection, and the voltage can be compensated in series.

[0088] The first switch (151) is turned ON when the smart transformer (100) is initially started, and can be kept in the ON state at all times when the distribution line (10, 50) is operating normally. If a short circuit occurs in either the first distribution line (10) or the second distribution line (50), both the first switch (151) and the second switch (155) can be turned OFF so that the accident in one distribution line does not spread to the other distribution line. In this case, the Y-connection connection with the secondary winding main winding (113) of the main transformer section (110) is severed, and since the connection of the secondary winding of the main transformer section (110) is open, the second distribution line (50) connected to the secondary winding can be disconnected from the smart transformer (100). Through this blocking function, it is possible to block the transmission of an emergency situation that occurs in the first distribution line (10) or the second distribution line.

[0090] In the embodiments of FIGS. 2 to 5 above, the main transformer section of the smart transformer according to the present invention is described as an example in which it is connected to the first distribution line in a delta connection manner and to the second distribution line in a Y connection manner. However, when additional transformers are applied as needed, the smart transformer may be arranged by applying a three-phase delta structure in series to both the first distribution line and the second distribution line.

[0091] In this regard, FIG. 6 illustrates a configuration diagram of another embodiment of a smart transformer connected between different distribution lines to control power flow according to the present invention, and FIG. 7 illustrates a circuit diagram of another embodiment of a smart transformer according to the present invention.

[0092] In describing the embodiments of FIGS. 6 and FIGS. 7 above, descriptions of parts that overlap with or are similar to the embodiments of FIGS. 2 to 4 examined earlier will be omitted.

[0093] In the embodiments of FIGS. 6 and 7 above, the primary winding of the main transformer section (110) of the smart transformer (200) is connected to the first distribution line (10) in a delta connection manner, and the main winding of the secondary winding of the main transformer section (110) can also be connected to the second distribution line (50) in a delta connection manner.

[0094] A switch unit (250) may be provided to selectively connect the smart transformer (200) to the wiring line (10, 50) depending on whether the smart transformer (200) controls power flow.

[0095] In addition, a voltage compensator (270) may be additionally placed between the main winding of the secondary winding of the main transformer section (110) and the second distribution line (50).

[0096] The voltage compensator (270) may be provided corresponding to each of the three phases R, S, and T, and the voltage compensator (270) may have its primary winding connected in a delta connection manner to the main winding of the secondary winding of the main transformer section (210) and to the second distribution line (50), and its secondary winding connected to the power conversion section (230) to provide a compensation voltage for each phase.

[0097] And the inverter (235) and filter (237) of the power conversion unit (230) may also be provided corresponding to each of the three phases R, S, and T.

[0098] The voltage compensator (270) can independently control the compensation voltage for each phase and can generate an electrically isolated compensation voltage. Through this voltage compensator (270), voltage imbalance on the distribution line can be compensated more easily.

[0100] Furthermore, as explained above, since the smart transformer according to the present invention can adjust the turn ratio of the primary and secondary sides of the main transformer section, it can control power flow even in situations where there is a large difference in voltage between two different distribution lines.

[0101] Existing UPFC and SOP methods have a problem in that they cannot be directly applied when the voltage difference between two distribution lines exceeds a certain level, such as in MV-LV distribution lines where there is a large difference in distribution voltage. However, the smart transformer proposed in this invention can be flexibly applied to each situation by changing the winding ratio of the transformer, even in situations where there is a large voltage difference between distribution lines.

[0103] In addition, the present invention presents a distribution system control system employing a smart transformer that controls power flow by connecting between different distribution lines as described above. In this regard, FIG. 8 illustrates a configuration diagram of an embodiment of a distribution system control system according to the present invention.

[0104] The transmission system (300) includes power generation facilities (310, 320, 330) and substations (350, 360), and these facilities can be interconnected in a complex manner by applying a mesh structure.

[0105] In contrast, the distribution system (400) can be configured in a unidirectional manner to supply power to consumers (500). For example, a 22.9kV distribution line that is drawn from a 154kV / 22.9kV substation (S / S; Sub Station) and supplies power to consumers may have a unidirectional radial structure.

[0106] The smart transformer presented in the present invention can be applied to various situations in a power distribution system (400), and three cases are presented and explained as examples.

[0107] As a first embodiment, the power flow of a distribution system can be controlled by applying a smart transformer (100a) according to the present invention to two selected distribution lines (412, 412) among a plurality of distribution lines connected from a main transformer facility Mtr (351) located in a substation A (350). In this case, if there is a large amount of renewable energy connected to one distribution line and it is necessary to divert energy to another adjacent line, power diversion becomes possible by applying a smart transformer (100a) according to the present invention.

[0108] As a second embodiment, the power flow of the distribution system can be controlled by applying the smart transformer (100b) according to the present invention to two selected distribution lines (412, 421) among a plurality of distribution lines connected from different main transformer facilities Mtr (351, 355) located in one substation A (350).

[0109] As a third embodiment, the power flow of the distribution system can be controlled by applying the smart transformer (100c) according to the present invention to two selected distribution lines (422, 431) among a plurality of distribution lines connected from main transformer facilities (355, 361) placed at each of different substations A (350) and B (360).

[0110] As such, by applying the present invention to various types of distribution networks, the power flow of the distribution lines can be controlled, thereby enabling the economical accommodation of increasing amounts of new and renewable energy without the need for additional expansion of distribution lines.

[0112] Through the invention described above, it becomes possible to control the power flow of two different distribution lines without changing the currently established distribution system or revising the operation process.

[0113] In particular, the present invention can provide an economical power flow control device for power distribution comprising a transformer with a multi-winding structure and a power converter with a small capacity relative to the transformer capacity. Furthermore, by combining a small-capacity power converter capable of active power control with a passive transformer that lacks control functions, power flow control that could not be performed with conventional transformers becomes possible.

[0115] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments described in the present invention are intended to explain, not limit, the technical concept of the present invention, and the technical concept of the present invention is not limited by these embodiments. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention. Explanation of the symbols

[0117] 100, 100a, 100b, 100c: Smart transformer, 110. 210: Main transformer section, 130, 230 : Power converter, 150, 250 : Switch section, 270 : Voltage compensator.

Claims

Claim 1 A smart transformer connected between different distribution lines to control power flow, characterized by being a multi-winding transformer in which the number of input terminals and the number of output terminals are adjusted, connected between the interruptions of a first distribution line and a second distribution line that supply power to a consumer, wherein the first distribution line is connected to a primary winding; a secondary winding including a main winding and an additional winding that are independently separated into two lines, wherein the second distribution line is connected to the main winding and a power converter is connected to the additional winding; a power converter having one end connected to the output terminal of the additional winding of the secondary winding and the other end connected to the output terminal of the main winding of the secondary winding to control power flow between the first distribution line and the second distribution line; and a switch unit that selectively connects the power converter to the main winding of the secondary winding according to the performance of a power flow function. Claim 2 A smart transformer connected between different distribution lines to control power flow, characterized in that, in claim 1, the first distribution line and the second distribution line supply three-phase power, and the main transformer section includes a primary winding connected to the first distribution line; and a secondary winding comprising a main winding and an additional winding configured to be separated into two wires for each phase of the three-phase power. Claim 3 A smart transformer connected between different distribution lines to control power flow, characterized in that, in claim 1, the main transformer section adjusts the winding ratio of the primary winding and the secondary winding based on the difference between the voltage of the first distribution line and the voltage of the second distribution line. Claim 4 A smart transformer that controls power flow connected between different distribution lines, characterized in that, in claim 2, the primary winding of the main transformer section is connected to the first distribution line in either a Y connection or a delta connection. Claim 5 A smart transformer that controls power flow connected between different distribution lines, characterized in that, in claim 2, the main winding of the main transformer section is connected to the second distribution line in either a Y connection or a delta connection, and the additional winding of the main transformer section is connected to the power converter in a delta connection. Claim 6 A smart transformer connected between different distribution lines to control power flow, characterized in that, in claim 2, the power conversion unit comprises: a rectifier, one side of which is connected to an additional winding of the secondary winding to convert AC to DC, and which receives active power required for power flow control from the additional winding to supply reactive power required for reactive power compensation; and an inverter, one side of which is connected to the other side of the rectifier and the other side of which is connected to the main winding of the secondary winding to convert DC to AC, and which adjusts an injection voltage required for power flow control and the phase angle of the injection voltage. Claim 7 A smart transformer connected between different distribution lines to control power flow, characterized in that, in claim 6, the power converter further comprises an inductor having one end connected to the output terminal of the inverter; and a filter having one end connected to the other end of the inductor and the other end connected to the main winding of the secondary winding. Claim 8 delete Claim 9 A smart transformer connected between different distribution lines to control power flow, characterized in that, in claim 7, the power converter further includes a DC link capacitor disposed between the rectifier and the inverter, and the switch unit includes: a first switch that selectively connects the filter to the main winding of the secondary winding; a second switch that selectively connects the neutral point of the DC link capacitor and the capacitor neutral point of the filter to the main winding of the secondary winding; and a switch controller that selectively operates the first switch and the second switch depending on whether power regulation is performed and whether a fault occurs in either the first distribution line or the second distribution line. Claim 10 A smart transformer connected between different distribution lines to control power flow, characterized in that, in claim 2, the primary winding is connected to the main winding of the main transformer section and the second distribution line, and the secondary winding is connected to the power converter section to provide a compensation voltage for each phase. Claim 11 A power distribution system control system characterized by comprising: a transmission system in which power generation facilities and substations are connected in a mesh structure; a distribution system comprising a plurality of separated distribution lines configured as one or more stages after the said substation to supply power to different consumers; and a smart transformer according to any one of claims 1 to 7, 9, and 10, which is connected between two different distribution line segments selected in the said distribution system to control the power flow of the distribution lines. Claim 12 A distribution system control system according to claim 11, characterized in that the two distribution lines to which the smart transformer is connected are selected from among a plurality of distribution lines connected from a single main transformer facility located in a single substation. Claim 13 A distribution system control system according to claim 11, characterized in that the two distribution lines to which the smart transformer is connected are selected from among a plurality of distribution lines each connected from different main transformer facilities located in a single substation. Claim 14 A distribution system control system according to claim 11, characterized in that the two distribution lines to which the smart transformer is connected are selected from among a plurality of distribution lines connected from respective main transformer facilities located at different substations.

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