On-load tap changer and method for controlling the same

Abstract

The application discloses a load tap changer and a control method thereof, which comprises a tap selector, five power electronic switches, two resistors and four mechanical switches. When the load tap changer is in a non-switching state, the first power electronic switch and the second power electronic switch are short-circuited by the first and third mechanical switches, the third power electronic switch is isolated by the fourth mechanical switch, or the first power electronic switch and the second power electronic switch are isolated by the third mechanical switch, and the third power electronic switch is short-circuited by the second and fourth mechanical switches. The two resistors can provide the on-voltage of the power electronic switch when the power electronic switch is turned on. When a transformer fails, the impact voltage generated by the transformer does not need to be borne by the power electronic switch, and the cost of the power electronic element is reduced as a whole. Only two main current flow switches and two switching switches are designed in the whole mechanical part, and the timing error caused by the mechanical switches as a whole is reduced. By arranging the two resistors, the arc breaking of the mechanical switch is realized.

Description

Technical Field

[0001] This invention relates to the field of transformer technology, and more specifically to an on-load tap changer and its control method. Background Technology

[0002] On-load tap changers (OLTCs) are the core components of power transformers for voltage regulation. On-load tap changer technology is a crucial means of stabilizing voltage; it involves switching the transformer from one tap to another without interrupting power, thereby adjusting the effective number of turns in the transformer windings to achieve voltage regulation. Currently, over 90% of power transformers ranging from 10 to 500 kV are equipped with mechanical on-load tap changers. Because mechanical on-load tap changers have numerous operating parts and long switching times, if the timing error between adjacent mechanical switches exceeds a preset value, it can lead to difficulties in extinguishing the arc, causing arc discharges of hundreds of kiloamperes on the tap changer, which can easily result in explosions and fires. To address these problems, replacing mechanical on-load tap changers with power electronic components has become a research hotspot, primarily encompassing two approaches: pure power electronic and hybrid mechanical-power electronic approaches.

[0003] Replacing mechanical tap changers with purely electronic on-load tap changers offers advantages such as arc-free switching and rapid operation. However, it requires a large number of power electronic devices, resulting in high costs. Furthermore, the long-term current flow of these devices necessitates additional water-cooling equipment, leading to significant losses and low reliability. Purely electronic on-load tap changers are currently in the theoretical research stage.

[0004] A hybrid mechanical and power electronic on-load tap changer is adopted, replacing the mechanical switching switch with a semi-controlled power electronic component, thus eliminating arcing during the switching process and extending the service life of the on-load tap changer. However, traditional hybrid on-load tap changers suffer from problems such as the long-term voltage stress tolerance of power electronic components during steady-state operation and the need for a large number of components connected in series. In addition, when triggering the power electronic component to turn on, the voltage applied across the power electronic component must exceed its threshold voltage to achieve turn-on. The voltage across the power electronic component is provided by the arcing of the mechanical switch, which leads to severe erosion of the mechanical switch contacts over long-term operation. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide an on-load tap changer and its control method to solve the technical problem in the prior art where the voltage across the power electronic components is provided by the arcing of a mechanical switch, and long-term operation leads to severe burning of the mechanical switch contacts.

[0006] The technical solutions provided by the embodiments of the present invention are as follows:

[0007] A first aspect of the present invention provides an on-load tap changer, comprising: a tap selector, a first power electronic switch, a second power electronic switch, a third power electronic switch, a fourth power electronic switch, a fifth power electronic switch, a first mechanical switch, a second mechanical switch, a third mechanical switch, a fourth mechanical switch, a first resistor, and a second resistor. The tap selector is connected to a transformer regulating winding. One end of the first mechanical switch is connected to a first terminal of the tap selector and one end of the third mechanical switch. The other end of the first mechanical switch is connected to one terminal of the fourth power electronic switch and one end of the first resistor. The other end of the fourth power electronic switch is connected to... The other end of the first resistor and the neutral point of the on-load tap changer; the other end of the third mechanical switch is connected to one end of the first power electronic switch and one end of the second power electronic switch, the other end of the first power electronic switch is connected to the other end of the second power electronic switch and the neutral point of the on-load tap changer; one end of the second mechanical switch is connected to the second end of the tap selector and one end of the fourth mechanical switch, the other end of the second mechanical switch is connected to one end of the fifth power electronic switch and one end of the second resistor, the other end of the fifth power electronic switch is connected to the other end of the second resistor and the neutral point of the on-load tap changer. The other end of the fourth mechanical switch is connected to one end of the third power electronic switch, and the other end of the third power electronic switch is connected to the neutral point of the on-load tap changer. When the on-load tap changer is in a non-switching state, the first mechanical switch is in a closed state, the second mechanical switch is in an open state, the third mechanical switch is in a closed state, and the fourth mechanical switch is in an open state. The first power electronic switch and the second power electronic switch are short-circuited by the first mechanical switch and the third mechanical switch, the third power electronic switch is isolated by the fourth mechanical switch, and the fourth power electronic switch is in a conducting state, with current flowing through the transformer windings. The first terminal of the tap selector, the first mechanical switch, and the fourth power electronic switch are connected to the neutral point of the on-load tap changer; or, the first mechanical switch is in the open state, the second mechanical switch is in the closed state, the third mechanical switch is in the open state, and the fourth mechanical switch is in the closed state, the first power electronic switch and the second power electronic switch are isolated by the third mechanical switch, the third power electronic switch is short-circuited by the second mechanical switch and the fourth mechanical switch, the fifth power electronic switch is in the on state, and the current flows through the transformer winding, the second terminal of the tap selector, the second mechanical switch, and the fifth power electronic switch to the neutral point of the on-load tap changer;

[0008] Optionally, the on-load tap changer further includes: a first insulating bushing, a second insulating bushing, a third insulating bushing, a fourth insulating bushing, a fifth insulating bushing, a sixth insulating bushing, and a seventh insulating bushing. The first insulating bushing is connected between the first mechanical switch and the fourth power electronic switch; the second insulating bushing is connected between the third mechanical switch and the first power electronic switch; the third insulating bushing is connected between the third mechanical switch and the second power electronic switch; the fourth insulating bushing is connected between the fourth mechanical switch and the third power electronic switch; the fifth insulating bushing is connected between the second mechanical switch and the fifth power electronic switch; the sixth insulating bushing is connected between the first terminal of the tap selector and the first mechanical switch and the third mechanical switch; and the seventh insulating bushing is connected between the second terminal of the tap selector and the second mechanical switch and the fourth mechanical switch.

[0009] Optionally, the on-load tap changer further includes a third resistor connected between the third mechanical switch and the second power electronic switch.

[0010] Optionally, the on-load tap changer further includes a surge arrester device disposed between the first and second terminals of the tap selector.

[0011] Optionally, any one of the first power electronic switch, the second power electronic switch, the third power electronic switch, the fourth power electronic switch, and the fifth power electronic switch includes: at least two anti-parallel thyristors; or, any one of the first power electronic switch, the second power electronic switch, the third power electronic switch, the fourth power electronic switch, and the fifth power electronic switch includes: at least two IGBTs and at least two diodes, wherein the IGBTs and diodes are connected in anti-parallel and the IGBTs are connected in series.

[0012] Optionally, any one of the first power electronic switch, the second power electronic switch, the third power electronic switch, the fourth power electronic switch, and the fifth power electronic switch includes: a capacitor and four IGBTs with anti-parallel diodes. The four IGBTs with anti-parallel diodes form a bridge structure, and the two sets of series-connected IGBTs are connected in parallel in the same direction and then connected in parallel with the capacitor.

[0013] Optionally, any one of the first power electronic switch, the second power electronic switch, the third power electronic switch, the fourth power electronic switch, and the fifth power electronic switch includes: a bridge rectifier circuit composed of an IGBT and four diodes, wherein two sets of series-connected diodes are connected in parallel in the same direction, and the IGBT is connected in parallel to the diodes in the same direction.

[0014] A second aspect of the present invention provides a control method for an on-load tap changer, the control method being applied to the on-load tap changer described in the first aspect and any one of the first aspects of the present invention, comprising: when the on-load tap changer is in a non-switching state, the first mechanical switch is in a closed state, the second mechanical switch is in an open state, the third mechanical switch is in a closed state, and the fourth mechanical switch is in an open state; the first power electronic switch and the second power electronic switch are short-circuited by the first mechanical switch and the third mechanical switch; the third power electronic switch is isolated by the fourth mechanical switch; the fourth power electronic switch is in a conducting state; and current flows through the transformer winding, the first terminal of the tap selector, the first mechanical switch, and the fourth power electronic switch to the neutral point of the on-load tap changer; or, the first mechanical switch is in an open state, the... When the second mechanical switch is closed, the third mechanical switch is open, and the fourth mechanical switch is closed, the first and second power electronic switches are isolated by the third mechanical switch, the third power electronic switch is short-circuited by the second and fourth mechanical switches, and the fifth power electronic switch is in the conducting state. Current flows through the transformer winding, the second terminal of the tap selector, the second mechanical switch, and the fifth power electronic switch to the neutral point of the on-load tap changer. When the on-load tap changer is in the switching state, the states of the first, second, third, and fourth mechanical switches are adjusted, and the first, second, third, fourth, or fifth power electronic switches are triggered to complete the switching between the two terminals of the on-load tap changer.

[0015] Optionally, when the on-load tap changer is in the switching state, the states of the first mechanical switch, the second mechanical switch, the third mechanical switch, and the fourth mechanical switch are adjusted, and the first power electronic switch, the second power electronic switch, the third power electronic switch, the fourth power electronic switch, or the fifth power electronic switch is triggered to complete the switching between the two terminals of the on-load tap changer. This includes: when switching the on-load tap changer, triggering the first power electronic switch to conduct, stopping the triggering of the fourth power electronic switch, the voltage on the first resistor providing the conduction voltage of the first power electronic switch, disconnecting the first mechanical switch, and the current flowing through the transformer winding, the first terminal of the tap selector, the third mechanical switch, and the first power electronic switch to the neutral point of the on-load tap changer; triggering the second... The power electronic switch stops triggering the first power electronic switch, and the current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch, and the second power electronic switch to the neutral point of the on-load tap changer; closing the fourth mechanical switch triggers the third power electronic switch to conduct; closing the second power electronic switch disconnects the third mechanical switch, and the current flows through the transformer winding, the second terminal of the tap selector, the fourth mechanical switch, and the third power electronic switch to the neutral point of the on-load tap changer; closing the second mechanical switch triggers the fifth power electronic switch to conduct, and closing the third power electronic switch, the current flows through the transformer winding, the second terminal of the tap selector, the second mechanical switch, and the fifth power electronic switch to the neutral point of the on-load tap changer, completing the switching process of the on-load tap changer from the first terminal to the second terminal.

[0016] Optionally, when the on-load tap changer is in the switching state, the states of the first, second, third, and fourth mechanical switches are adjusted, and the first, second, third, fourth, or fifth power electronic switches are triggered to complete the switching between the two terminals of the on-load tap changer. This includes: when switching the on-load tap changer, triggering the third power electronic switch to conduct, stopping the triggering of the fifth power electronic switch, the voltage on the second resistor providing the conduction voltage of the third power electronic switch, disconnecting the second mechanical switch, and the current flowing through the transformer winding, the second terminal of the tap selector, the fourth mechanical switch, and the third power electronic switch to the neutral point of the on-load tap changer; closing the third mechanical switch, and disconnecting the second mechanical switch. The second mechanical switch triggers the second power electronic switch to conduct; the third power electronic switch is turned off, and the current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch, and the second power electronic switch to the neutral point of the on-load tap changer; the first power electronic switch is triggered to conduct, and the second power electronic switch is turned off, and the current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch, and the first power electronic switch to the neutral point of the on-load tap changer; the fourth mechanical switch is opened, the first mechanical switch is closed, the fourth power electronic switch is triggered to conduct, and the first power electronic switch is turned off, and the current flows through the transformer winding, the first terminal of the tap selector, the first mechanical switch, and the fourth power electronic switch to the neutral point of the on-load tap changer, completing the switching process of the on-load tap changer from the second terminal to the first terminal.

[0017] The technical solution of this invention has the following advantages:

[0018] The on-load tap changer and its control method provided in this invention, by setting a first mechanical switch and a second mechanical switch as the main current-carrying switches, ensures that the intermediate third and fourth mechanical switches, as well as the three power electronic switches that perform the switching function, do not bear high voltage and current stress during normal transformer operation and tap adjustment. This solves the problem of excessive series connection of power electronic components, reducing the overall cost of the on-load tap changer. Furthermore, the on-load tap changer only requires two main current-carrying switches and two switching switches in its entire mechanical part, thereby reducing the timing errors caused by the mechanical switches and the timing coordination requirements of the mechanical switches during switching. In addition, by setting a first resistor and a second resistor, the conduction voltage of the power electronic switches is provided by the resistors, not by the arcing of the mechanical switches, thus solving the problem of contact erosion of the mechanical switches. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a structural block diagram of an on-load tap changer in an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the structure of five power electronic switches in an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the structure of five power electronic switches in another embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of the structure of five power electronic switches in another embodiment of the present invention;

[0024] Figure 5 This is a schematic diagram of the structure of five power electronic switches in another embodiment of the present invention;

[0025] Figure 6 This is a flowchart of the control method for an on-load tap changer in an embodiment of the present invention;

[0026] Figures 7(a) to 7(f) This is a schematic diagram of the on-load tap changer switching process in an embodiment of the present invention;

[0027] Figure 8 This is a schematic diagram of the control timing of the on-load tap changer in an embodiment of the present invention;

[0028] Figure 9 This is a schematic diagram of the control timing of an on-load tap changer in another embodiment of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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 limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] This invention provides an on-load tap changer, such as... Figure 1As shown, the on-load tap changer includes: a tap selector, a first power electronic switch 701, a second power electronic switch 702, a third power electronic switch 703, a fourth power electronic switch 801, a fifth power electronic switch 802, a first mechanical switch 100, a second mechanical switch 200, a third mechanical switch 300, a fourth mechanical switch 400, a first resistor 901, and a second resistor 902. The tap selector is connected to the voltage regulating winding of the transformer. One end of the first mechanical switch 100 is connected to the first terminal 1 of the tap selector and one end of the third mechanical switch 300, and the other end of the first mechanical switch 100 is connected to one terminal of the fourth power electronic switch 801. The first power electronic switch 701 is connected to one end of the first power electronic switch 901, and the other end of the fourth power electronic switch 801 is connected to the other end of the first power electronic switch 901 and the neutral point of the on-load tap changer; the other end of the third mechanical switch 300 is connected to one end of the first power electronic switch 701 and one end of the second power electronic switch 702, and the other end of the first power electronic switch 701 is connected to the other end of the second power electronic switch 702 and the neutral point of the on-load tap changer; one end of the second mechanical switch 200 is connected to the second terminal of the tap selector and one end of the fourth mechanical switch 400, and the other end of the second mechanical switch 200 is connected to the fifth power electronic switch 701. One end of switch 802 and one end of the second resistor 902 are connected; the other end of the fifth power electronic switch 802 is connected to the other end of the second resistor 902 and the neutral point of the on-load tap changer; the other end of the fourth mechanical switch 400 is connected to one end of the third power electronic switch 703, and the other end of the third power electronic switch 703 is connected to the neutral point of the on-load tap changer; when the on-load tap changer is in a non-switching state, the first mechanical switch 100 is in a closed state, the second mechanical switch 200 is in an open state, the third mechanical switch 300 is in a closed state, and the fourth mechanical switch 400 is in an open state. Sub-switch 701 and the second power electronic switch 702 are short-circuited by the first mechanical switch 100 and the third mechanical switch 300, and the third power electronic switch 703 is isolated by the fourth mechanical switch 400; or, the first mechanical switch 100 is in the open state, the second mechanical switch 200 is in the closed state, the third mechanical switch 300 is in the open state, and the fourth mechanical switch 400 is in the closed state, and the third power electronic switch 703 is short-circuited by the second mechanical switch 200 and the fourth mechanical switch 400, and the first power electronic switch 701 and the second power electronic switch 702 are isolated by the third mechanical switch 300. The output terminal of the on-load tap changer can be used as the neutral point of the on-load tap changer.

[0033] Specifically, when the on-load tap changer is in a non-switching state, the first mechanical switch 100 and the third mechanical switch 300 are closed, the second mechanical switch 200 and the fourth mechanical switch 400 are open, and the fourth power electronic switch 801 is on; or the first mechanical switch 100 and the third mechanical switch 300 are open, the second mechanical switch 200 and the fourth mechanical switch 400 are closed, and the fifth power electronic switch 802 is on. Thus, the closed first mechanical switch 100 and the third mechanical switch 300 short-circuit their connected power electronic switches 701 and 702, and the open fourth mechanical switch 400 isolates its connected power electronic switch 703. Alternatively, the closed second mechanical switch 200 and the fourth mechanical switch 400 short-circuit their connected power electronic switch 703, and the open third mechanical switch 300 isolates its connected power electronic switches 701 and 702. The current flows through the transformer winding, the first terminal of the tap selector, the first mechanical switch, and the fourth power electronic switch to the neutral point of the on-load tap changer; or the current flows through the transformer winding, the second terminal of the tap selector, the second mechanical switch, and the fifth power electronic switch to the neutral point of the on-load tap changer.

[0034] Through the above connection method, the mechanical switch isolates the power electronic switch from the transformer unit point. During the operation of the transformer, the fault surge voltage generated directly at the two ports of the tap selector is borne by the mechanical switch, while the power electronic switch does not need to bear it. This avoids the power electronic switch from being subjected to overvoltage and overcurrent stress surges under normal transformer operation and fault conditions.

[0035] Furthermore, in this embodiment, when switching occurs, the on-state voltage of the first power electronic switch 701 is provided by the first resistor 901. When the first mechanical switch 100 is closed, and the fourth power electronic switch 801 is turned off while the first power electronic switch 701 is turned on, current flows through the third mechanical switch 300 and the first power electronic switch 701 to the neutral point of the on-load tap changer. Thus, the first mechanical switch 100 is disconnected without current, preventing arcing and avoiding contact erosion. Similarly, the on-state voltage of the third power electronic switch 703 is provided by the second resistor 902. When the second mechanical switch 200 is closed, and the fifth power electronic switch 802 is turned off while the third power electronic switch 703 is turned on, current flows through the fourth mechanical switch 400 and the third power electronic switch 703 to the neutral point of the on-load tap changer. That is, the second mechanical switch 200 is disconnected without current, preventing arcing and avoiding contact erosion. Therefore, the first and second resistors form an arc-free transition circuit, enabling arc-free breaking of the mechanical switch, avoiding contact erosion caused by electric arc, and improving the service life of the equipment.

[0036] The on-load tap changer provided in this embodiment of the invention uses a first mechanical switch 100 and a second mechanical switch 200 as the main current-carrying switches. This ensures that the intermediate third mechanical switch 300, fourth mechanical switch 400, and the three power electronic switches responsible for switching do not experience high voltage or current stress during normal transformer operation and tap adjustment. This solves the problem of excessive series connection of power electronic components, reducing the overall cost of the on-load tap changer. Furthermore, the on-load tap changer only uses two main current-carrying switches and two switching switches in its entire mechanical part. This reduces the timing errors caused by the mechanical switches and the timing coordination requirements of the mechanical switches during switching. In addition, the use of a first resistor 901 and a second resistor 902 ensures that the conduction voltage of the power electronic switches is provided by the resistors, not by the arcing of the mechanical switches, thus solving the problem of contact erosion of the mechanical switches.

[0037] In one embodiment, such as Figure 1 As shown, the on-load tap changer further includes: a first insulating bushing 601, a second insulating bushing 602, a third insulating bushing 603, a fourth insulating bushing 604, a fifth insulating bushing 605, a sixth insulating bushing 606, and a seventh insulating bushing 607. The first insulating bushing 601 is connected between the first mechanical switch 100 and the fourth power electronic switch 701; the second insulating bushing 602 is connected between the third mechanical switch 300 and the first power electronic switch 701; the third insulating bushing 603 is connected between the third mechanical switch 300 and the second power electronic switch 701. The fourth insulating sleeve 604 is connected between the fourth mechanical switch 400 and the third power electronic switch 703; the fifth insulating sleeve 605 is connected between the second mechanical switch 200 and the fifth power electronic switch 802; the sixth insulating sleeve 606 is connected between the first end of the tap selector and the first mechanical switch 100 and the third mechanical switch 300; the seventh insulating sleeve 607 is connected between the second end of the tap selector and the second mechanical switch 200 and the fourth mechanical switch 400.

[0038] In one embodiment, such as Figure 1 As shown, the on-load tap changer further includes a third resistor 500, which is connected between the third mechanical switch 300 and the second power electronic switch 702. In one specific embodiment, the third resistor 500 serves as a current-limiting resistor, which can suppress the circulating current generated between the second power electronic switch 702 and the third power electronic switch 703 during the switching process, thereby effectively protecting the second power electronic switch 702 and the third power electronic switch 703.

[0039] In one embodiment, such as Figure 1As shown, the on-load tap changer also includes a surge arrester device 60, which is disposed between the first and second terminals of the tap selector. Specifically, the surge arrester device 60 can be a surge arrester resistor or other surge arrester devices; this invention does not limit this selection. The surge arrester device installed in the on-load tap changer can protect the first power electronic switch 701, the second power electronic switch 702, and the third power electronic switch 703, which perform the switching function, from transient overvoltage impacts, forming double protection for the three power electronic switches.

[0040] In one embodiment, such as Figure 2 As shown, any one of the first power electronic switch 701, the second power electronic switch 702, the third power electronic switch 703, the fourth power electronic switch 801, and the fifth power electronic switch 802 includes at least two anti-parallel thyristors 71 and 72, thereby conducting and interrupting bidirectional alternating current.

[0041] In one embodiment, such as Figure 3 As shown, any one of the first power electronic switch 701, the second power electronic switch 702, the third power electronic switch 703, the fourth power electronic switch 801, and the fifth power electronic switch 802 includes: at least two insulated gate bipolar transistors (IGBTs) 75 and 76 and at least two diodes 73 and 74, wherein the IGBTs and diodes are connected in anti-parallel and the IGBTs are connected in series, thereby conducting and interrupting bidirectional alternating current.

[0042] In one embodiment, such as Figure 4 As shown, any one of the first power electronic switch 701, the second power electronic switch 702, the third power electronic switch 703, the fourth power electronic switch 801, and the fifth power electronic switch 802 includes: a capacitor 78 and four IGBTs 77 with anti-parallel diodes. The four IGBTs 77 with anti-parallel diodes form a bridge structure, wherein every two IGBTs 77 with anti-parallel diodes are connected in series in the same direction, and the connection point serves as a lead-out node. The two sets of series-connected IGBTs 77 are connected in parallel in the same direction and then connected in parallel with the capacitor 78, thereby conducting and interrupting bidirectional alternating current.

[0043] In one embodiment, such as Figure 5As shown, any one of the first power electronic switch 701, the second power electronic switch 702, the third power electronic switch 703, the fourth power electronic switch 801, and the fifth power electronic switch 802 includes a bridge rectifier circuit composed of an IGBT 79 and four diodes 80. Two sets of series-connected diodes 80 are connected in parallel in the same direction, and the IGBT 79 is connected in parallel with the diodes 80 in the same direction. Its collector is connected to the diode cathode, and its emitter is connected to the diode anode, thereby conducting and interrupting bidirectional alternating current, while ensuring that the IGBT device always withstands a forward voltage drop, thus protecting the IGBT.

[0044] Specifically, the first power electronic switch 701, the second power electronic switch 702, the third power electronic switch 703, the fourth power electronic switch 801, or the fifth power electronic switch 802 can be configured according to the structure provided in the above embodiments. That is, the first power electronic switch 701, the second power electronic switch 702, the third power electronic switch 703, the fourth power electronic switch 801, or the fifth power electronic switch 802 can select the same structure or different structures according to the above embodiments. The embodiments of the present invention do not limit this.

[0045] In this embodiment, such as Figure 1 As shown, the tap selector, first mechanical switch 100, second mechanical switch 200, third mechanical switch 300, and fourth mechanical switch 400 are disposed inside the transformer, while the first power electronic switch 701, second power electronic switch 702, third power electronic switch 703, fourth power electronic switch 801, fifth power electronic switch 802, first resistor 901, and second resistor 902 are disposed outside the transformer. Specifically, the tap selector is disposed inside the transformer and connected to the transformer's regulating winding. The lightning protection device 60, third resistor 500, first mechanical switch 100, second mechanical switch 200, third mechanical switch 300, and fourth mechanical switch 400 are disposed inside the oil chamber, while the first power electronic switch 701, second power electronic switch 702, third power electronic switch 703, fourth power electronic switch 801, fifth power electronic switch 802, first resistor 901, and second resistor 902 are disposed outside the transformer.

[0046] This invention also provides a control method for an on-load tap changer, which is applied to the on-load tap changer described in the above embodiments, such as... Figure 6 As shown, the control method includes the following steps:

[0047] Step S101: When the on-load tap changer is in a non-switching state, the first mechanical switch 100 is closed, the second mechanical switch 200 is open, the third mechanical switch 300 is closed, and the fourth mechanical switch 400 is open. The first power electronic switch 701 and the second power electronic switch 702 are short-circuited by the first mechanical switch 100 and the third mechanical switch 300. The third power electronic switch 703 is isolated by the fourth mechanical switch 400. The fourth power electronic switch 801 is in a conducting state. Current flows through the first terminal 1 of the tap selector, the first mechanical switch 100, and the fourth power electronic switch 801 to the neutral point of the on-load tap changer. As shown in Figure 7(a); or, the first mechanical switch 100 is in the open state, the second mechanical switch 200 is in the closed state, the third mechanical switch 300 is in the open state and the fourth mechanical switch 400 is in the closed state, the first power electronic switch 701 and the second power electronic switch 702 are isolated by the third mechanical switch 300, the third power electronic switch 703 is short-circuited by the second mechanical switch 200 and the fourth mechanical switch 400, the fifth power electronic switch 802 is in the on-load tap changer neutral point through the second terminal 2 of the tap selector, the second mechanical switch 200 and the fifth power electronic switch 802, as shown in Figure 7(f).

[0048] Step S102: When the on-load tap changer is in the switching state, adjust the state of the first mechanical switch 100, the second mechanical switch 200, the third mechanical switch 300 and the fourth mechanical switch 400, and trigger the first power electronic switch 701, the second power electronic switch 702, the third power electronic switch 703, the fourth power electronic switch 801 or the fifth power electronic switch 802 to complete the switching between the two terminals of the on-load tap changer.

[0049] The on-load tap changer control method provided in this invention uses a first mechanical switch 100 and a second mechanical switch 200 as main current-carrying switches. This ensures that the intermediate third mechanical switch 300, fourth mechanical switch 400, and the three power electronic switches responsible for switching do not experience high voltage or current stress during normal transformer operation and tap adjustment. This solves the problem of excessive series connection of power electronic components, reducing the overall cost of the on-load tap changer. Furthermore, the on-load tap changer only uses two main current-carrying switches and two switching switches in its mechanical components. This reduces the timing errors caused by the mechanical switches and the timing coordination requirements during switching. In addition, the use of a first resistor 901 and a second resistor 902 ensures that the conduction voltage of the power electronic switches is provided by the resistors, not by the arcing of the mechanical switches, thus solving the problem of contact erosion of the mechanical switches.

[0050] In one embodiment, when the on-load tap changer needs to switch from the first terminal to the second terminal of the tap selector, the switching of the on-load tap changer can be achieved according to the following process: when the on-load tap changer is in the switching state, the states of the first mechanical switch 100, the second mechanical switch 200, the third mechanical switch 300, and the fourth mechanical switch 400 are adjusted, and the first power electronic switch 701, the second power electronic switch 702, the third power electronic switch 703, the fourth power electronic switch 801, or the fifth power electronic switch 802 is triggered to complete the switching between the two terminals of the on-load tap changer, including the following steps:

[0051] Step S201: When the tap changer is switched, as shown in Figure 7(b), the first power electronic switch 701 is triggered to turn on, and the fourth power electronic switch 801 is stopped from being triggered. The voltage on the first resistor 901 provides the turn-on voltage for the first power electronic switch 701, and the first mechanical switch 100 is turned off. The current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch 300 and the first power electronic switch 701 to the neutral point of the on-load tap changer.

[0052] Step S202: As shown in Figure 7(c), the second power electronic switch 702 is triggered and the first power electronic switch 701 is stopped. The current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch 300 and the second power electronic switch 702 to the neutral point of the on-load tap changer.

[0053] Step S203: As shown in Figure 7(d), closing the fourth mechanical switch 400 triggers the third power electronic switch 703 to conduct. When the fourth mechanical switch 400 is closed, the first power electronic switch 701 is turned off, and the third power electronic switch 703 is turned on, a circulating current will occur between the third power electronic switch 703 and the second power electronic switch 702 due to the voltage difference between the first and second terminals of the tap selector. Therefore, by placing a third resistor 500 between the third mechanical switch 300 and the second power electronic switch 702, this circulating current can be suppressed, preventing damage to the two power electronic switches. Simultaneously, as... Figure 8 As shown, for the fourth mechanical switch 400, stable switching of the tap changer can be achieved as long as it is closed before triggering the third power electronic switch 703. That is, the action of closing the fourth mechanical switch 400 can be completed at any point in time between the start of switching and the triggering of the third power electronic switch 703.

[0054] Step S204: As shown in Figure 7(e), turn off the second power electronic switch 702, disconnect the third mechanical switch 300, and the current flows through the transformer winding, the second terminal of the tap selector, the fourth mechanical switch 400, and the third power electronic switch 703 to the neutral point of the on-load tap changer; specifically, as shown in Figure 7(e), Figure 8 As shown, the third mechanical switch 300 can be disconnected as soon as the second power electronic switch 702 is turned off. That is, the action of disconnecting the third mechanical switch 300 can be completed at any time after the second power electronic switch 702 is turned off and before the switching process between the first terminal and the second terminal is completed.

[0055] Step S205: As shown in Figure 7(f), close the second mechanical switch 200, trigger the fifth power electronic switch 802 to conduct, and turn off the third power electronic switch 703. The current flows through the transformer winding, the second terminal of the tap selector, the second mechanical switch 200 and the fifth power electronic switch 802 to the neutral point of the on-load tap changer, completing the switching process of the on-load tap changer from the first terminal to the second terminal.

[0056] In one embodiment, when the on-load tap changer needs to switch from the second terminal to the first terminal of the tap selector, the switching of the on-load tap changer can be achieved according to the following process: when the on-load tap changer is in the switching state, the states of the first mechanical switch 100, the second mechanical switch 200, the third mechanical switch 300, and the fourth mechanical switch 400 are adjusted, and the first power electronic switch 701, the second power electronic switch 702, the third power electronic switch 703, the fourth power electronic switch 801, or the fifth power electronic switch 802 is triggered to complete the switching between the two terminals of the on-load tap changer, including the following steps:

[0057] Step S301: When the on-load tap changer switches, the third power electronic switch 703 is triggered to turn on, and the fifth power electronic switch 802 is stopped from being triggered. The voltage on the second resistor 902 provides the turn-on voltage for the third power electronic switch 703, and the second mechanical switch 200 is turned off. The current flows through the transformer winding, the second terminal of the tap selector, the fourth mechanical switch 400, and the third power electronic switch 703 to the neutral point of the on-load tap changer.

[0058] Step S302: Close the third mechanical switch 300, triggering the second power electronic switch 702 to conduct. Specifically, when the third mechanical switch 300 is closed and the second power electronic switch 702 is conducted, a circulating current will be generated between the third power electronic switch 703 and the second power electronic switch 702 due to the voltage difference between the first and second terminals of the tap selector. Therefore, by placing a third resistor 500 between the third mechanical switch 300 and the second power electronic switch 702, this circulating current can be suppressed, preventing damage to the two power electronic switches. Meanwhile, as... Figure 9 As shown, for the third mechanical switch 300, stable switching of the tap changer can be achieved as long as it is closed before triggering the second power electronic switch 702. That is, the action of closing the third mechanical switch 300 can be completed at any point in time between the start of switching and the triggering of the second power electronic switch 702.

[0059] Step S303: Turn off the third power electronic switch 703. Current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch 300, and the second power electronic switch 702 to the neutral point of the on-load tap changer.

[0060] Step S304: Trigger the first power electronic switch 701 to turn on and the second power electronic switch 702 to turn off. Current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch and the first power electronic switch 701 to the neutral point of the on-load tap changer.

[0061] Step S305: Disconnect the fourth mechanical switch 400, close the first mechanical switch 100, trigger the fourth power electronic switch 801 to conduct, and disconnect the first power electronic switch 701. Current flows through the transformer winding, the first terminal of the tap selector, the first mechanical switch 100, and the fourth power electronic switch 801 to the neutral point of the on-load tap changer, completing the switching process of the on-load tap changer from the second terminal to the first terminal. Specifically, as follows... Figure 9 As shown, the action of disconnecting the fourth mechanical switch 400 can be performed as soon as the first power electronic switch 701 is triggered. That is, the action of disconnecting the fourth mechanical switch 400 can be completed at any time after the first power electronic switch 701 is triggered and before the switching process between the second terminal and the first terminal is completed.

[0062] Figure 8 A timing diagram of the switching process of the on-load tap changer from the first terminal to the second terminal is given. Figure 9A timing diagram of the switching process of the on-load tap changer from the second terminal to the first terminal is provided. As can be seen from the diagram, whether switching the on-load tap changer from the first terminal to the second terminal or vice versa, the third mechanical switch 300 and the fourth mechanical switch 400 only need to operate before or after the operating time shown in the diagram. Therefore, the control method for the on-load tap changer provided in this embodiment of the invention has lower requirements for the timing coordination of the third mechanical switch 300 and the fourth mechanical switch 400, reducing the difficulty of timing coordination during the switching process.

[0063] While exemplary embodiments and their advantages have been described in detail, those skilled in the art can make various changes, substitutions, and modifications to these embodiments without departing from the spirit of the invention and the scope of protection defined by the appended claims. Such modifications and variations all fall within the scope defined by the appended claims. For other examples, those skilled in the art should readily understand that the order of process steps can be changed while remaining within the scope of the invention.

Claims

1. An on-load tap changer, characterized in that, include: Tap selector, first power electronic switch, second power electronic switch, third power electronic switch, fourth power electronic switch, fifth power electronic switch, first mechanical switch, second mechanical switch, third mechanical switch, fourth mechanical switch, first resistor and second resistor; The tap selector is connected to the transformer's voltage regulating winding; One end of the first mechanical switch is connected to the first end of the tap selector and one end of the third mechanical switch. The other end of the first mechanical switch is connected to one end of the fourth power electronic switch and one end of the first resistor. The other end of the fourth power electronic switch is connected to the other end of the first resistor and the neutral point of the on-load tap changer. The other end of the third mechanical switch is connected to one end of the first power electronic switch and one end of the second power electronic switch, and the other end of the first power electronic switch is connected to the other end of the second power electronic switch and the neutral point of the on-load tap changer. One end of the second mechanical switch is connected to the second end of the tap selector and one end of the fourth mechanical switch; the other end of the second mechanical switch is connected to one end of the fifth power electronic switch and one end of the second resistor; the other end of the fifth power electronic switch is connected to the other end of the second resistor and the neutral point of the on-load tap changer. The other end of the fourth mechanical switch is connected to one end of the third power electronic switch, and the other end of the third power electronic switch is connected to the neutral point of the on-load tap changer. When the on-load tap changer is in a non-switching state, the first mechanical switch is closed, the second mechanical switch is open, the third mechanical switch is closed, and the fourth mechanical switch is open. The first power electronic switch and the second power electronic switch are short-circuited by the first and third mechanical switches, the third power electronic switch is isolated by the fourth mechanical switch, and the fourth power electronic switch is in a conducting state. Current flows through the transformer winding, the first terminal of the tap selector, the first mechanical switch, and the fourth power electronic switch to the neutral point of the on-load tap changer. Alternatively, the first mechanical switch is open, the second mechanical switch is closed, the third mechanical switch is open, and the fourth mechanical switch is closed. The first power electronic switch and the second power electronic switch are isolated by the third mechanical switch, the third power electronic switch is short-circuited by the second and fourth mechanical switches, and the fifth power electronic switch is in a conducting state. Current flows through the transformer winding, the second terminal of the tap selector, the second mechanical switch, and the fifth power electronic switch to the neutral point of the on-load tap changer. When the on-load tap changer is in the switching state, the states of the first, second, third, and fourth mechanical switches are adjusted, and the first, second, third, fourth, or fifth power electronic switches are triggered to complete the switching between the two ends of the on-load tap changer; wherein, The first resistor is used to provide a turn-on voltage to the first power electronic switch, so that the first mechanical switch is turned off in a zero-current state; The second resistor is used to provide a conduction voltage to the third power electronic switch, so that the second mechanical switch is turned off in a zero-current state.

2. The on-load tap changer according to claim 1, characterized in that, Also includes: A first insulating sleeve, a second insulating sleeve, a third insulating sleeve, a fourth insulating sleeve, a fifth insulating sleeve, a sixth insulating sleeve, and a seventh insulating sleeve are provided. The first insulating sleeve is connected between the first mechanical switch and the fourth power electronic switch; the second insulating sleeve is connected between the third mechanical switch and the first power electronic switch; the third insulating sleeve is connected between the third mechanical switch and the second power electronic switch; the fourth insulating sleeve is connected between the fourth mechanical switch and the third power electronic switch; the fifth insulating sleeve is connected between the second mechanical switch and the fifth power electronic switch; the sixth insulating sleeve is connected between the first terminal of the tap selector and the first mechanical switch and the third mechanical switch; and the seventh insulating sleeve is connected between the second terminal of the tap selector and the second mechanical switch and the fourth mechanical switch.

3. The on-load tap changer according to claim 1, characterized in that, Also includes: A third resistor is connected between the third mechanical switch and the second power electronic switch.

4. The on-load tap changer according to claim 1, characterized in that, Also includes: A surge arrester device, wherein the surge arrester device is disposed between the first and second terminals of the tap selector.

5. The on-load tap changer according to claim 1, characterized in that, The first power electronic switch, the second power electronic switch, the third power electronic switch, the fourth power electronic switch, and the fifth power electronic switch each include: at least two thyristors connected in anti-parallel; Alternatively, any one of the first power electronic switch, the second power electronic switch, the third power electronic switch, the fourth power electronic switch, and the fifth power electronic switch includes: at least two IGBTs and at least two diodes, wherein the IGBTs and diodes are connected in anti-parallel and the IGBTs are connected in series.

6. The on-load tap changer according to claim 1, characterized in that, Any one of the first power electronic switch, the second power electronic switch, the third power electronic switch, the fourth power electronic switch, and the fifth power electronic switch includes: a capacitor and four IGBTs with anti-parallel diodes. The four IGBTs with anti-parallel diodes form a bridge structure, and two sets of series-connected IGBTs are connected in parallel in the same direction and then connected in parallel with the capacitor.

7. The on-load tap changer according to claim 1, characterized in that, Any one of the first power electronic switch, the second power electronic switch, the third power electronic switch, the fourth power electronic switch, and the fifth power electronic switch includes: a bridge rectifier circuit composed of an IGBT and four diodes, with two sets of series-connected diodes connected in parallel in the same direction, and the IGBT connected in parallel to the diodes in the same direction.

8. A control method for an on-load tap changer, characterized in that, The control method is applied to the on-load tap changer according to any one of claims 1-7, comprising: When the on-load tap changer is in a non-switching state, the first mechanical switch is closed, the second mechanical switch is open, the third mechanical switch is closed, and the fourth mechanical switch is open. The first and second power electronic switches are short-circuited by the first and third mechanical switches, the third power electronic switch is isolated by the fourth mechanical switch, and the fourth power electronic switch is in a conducting state. Current flows through the transformer winding, the first terminal of the tap selector, the first mechanical switch, and the fourth power electronic switch to the neutral point of the on-load tap changer. Alternatively, the first mechanical switch is open, the second mechanical switch is closed, the third mechanical switch is open, and the fourth mechanical switch is closed. The first and second power electronic switches are isolated by the third mechanical switch, the third power electronic switch is short-circuited by the second and fourth mechanical switches, and the fifth power electronic switch is in a conducting state. Current flows through the transformer winding, the second terminal of the tap selector, the second mechanical switch, and the fifth power electronic switch to the neutral point of the on-load tap changer.

9. The control method according to claim 8, characterized in that, When the on-load tap changer is in the switching state, the states of the first, second, third, and fourth mechanical switches are adjusted, and the first, second, third, fourth, or fifth power electronic switches are triggered to complete the switching between the two ends of the on-load tap changer, including: When switching the on-load tap changer, the first power electronic switch is triggered to turn on, and the fourth power electronic switch is stopped from being triggered. The voltage on the first resistor provides the turn-on voltage for the first power electronic switch, and the first mechanical switch is turned off. The current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch, and the first power electronic switch to the neutral point of the on-load tap changer. The second power electronic switch is triggered to turn on, and the first power electronic switch is stopped from being triggered. The current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch and the second power electronic switch to the neutral point of the on-load tap changer. Closing the fourth mechanical switch triggers the third power electronic switch to turn on. Turn off the second power electronic switch and disconnect the third mechanical switch. The current flows through the transformer winding, the second terminal of the tap selector, the fourth mechanical switch and the third power electronic switch to the neutral point of the on-load tap changer. When the second mechanical switch is closed, the fifth power electronic switch is triggered to turn on, and the third power electronic switch is turned off. The current flows through the transformer winding, the second terminal of the tap selector, the second mechanical switch, and the fifth power electronic switch to the neutral point of the on-load tap changer, completing the switching process of the on-load tap changer from the first terminal to the second terminal.

10. The control method according to claim 8, characterized in that, When the on-load tap changer is in the switching state, the states of the first, second, third, and fourth mechanical switches are adjusted, and the first, second, third, fourth, or fifth power electronic switches are triggered to complete the switching between the two ends of the on-load tap changer, including: When switching the on-load tap changer, the third power electronic switch is triggered and the fifth power electronic switch is stopped. The voltage on the second resistor provides the conduction voltage of the third power electronic switch, and the second mechanical switch is disconnected. The current flows through the transformer winding, the second terminal of the tap selector, the fourth mechanical switch and the third power electronic switch to the neutral point of the on-load tap changer. Closing the third mechanical switch triggers the second power electronic switch to turn on. When the third power electronic switch is turned off, the current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch and the second power electronic switch to the neutral point of the on-load tap changer. The first power electronic switch is triggered to turn on, the second power electronic switch is turned off, and the current flows through the transformer winding, the first terminal of the tap selector, the third mechanical switch and the first power electronic switch to the neutral point of the on-load tap changer. Disconnect the fourth mechanical switch, close the first mechanical switch, trigger the fourth power electronic switch to turn on, and turn off the first power electronic switch. The current flows through the transformer winding, the first terminal of the tap selector, the first mechanical switch, and the fourth power electronic switch to the neutral point of the on-load tap changer, completing the switching process of the on-load tap changer from the second terminal to the first terminal.

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