A power electronic on-load tap changer and switching method thereof

Abstract

The present invention discloses a power electronic on-load tap changer and a switching method thereof, relating to the technical field of high-end electrical equipment manufacturing. The power electronic on-load tap changer comprises: a first load branch, one end of which is connected to a transformer tap N and the other end to a load; the first load branch comprises a main current-passing switch M1 and a first switching branch connected in parallel therewith, the first switching branch comprising an isolating switch T1 and a thyristor assembly SCR1; the isolating switch T1 having one end connected to the load via the thyristor assembly SCR1 and the other end switching between transformer taps N and N+1; and a switching branch comprising an isolating switch T3 and a thyristor assembly SCR3; the isolating switch T3 having one end connected to the load via the thyristor assembly SCR3 and the other end switching between transformer taps N and N+1. The present invention ensures relatively balanced erosion of the two thyristors, thereby increasing the service life of the tap changer.

Description

Technical Field

[0001] The present invention relates to the technical field of high-end electrical equipment manufacturing, and in particular to a power electronic on-load tap changer and a switching method thereof. Background Art

[0002] With the development of power electronic devices, nonlinear electronic devices have been widely used. The development of the power grid inevitably brings a series of new problems, and power quality issues are becoming increasingly serious. The voltage-regulating transformer is a key component for improving power quality, and the power electronic on-load tap-changer is a key element in realizing its function. It maintains a constant output voltage by changing the transformer's turns ratio. According to user needs, the power electronic on-load tap-changer needs to rely on a special transition circuit to switch between taps in the transformer without interrupting the load current, thereby ultimately changing the output voltage. With the advancement of technology, the power electronic on-load tap-changer combines the advantages of mechanical and power electronic devices, using power electronic devices to switch the current on and off. It has the characteristics of fast switching speed and arc-free switching. It has become a research focus in recent years and has achieved rapid development.

[0003] During the tap changer switching process, circulating current is a critical issue that must be addressed. To ensure continuous output current, there is a moment when both taps are simultaneously powered. Since the two taps have different potentials, circulating current is bound to occur between them. To comply with circuit principles, the two taps cannot be directly connected at the moment of simultaneous power supply. During the switching process, circulating current must be kept below a certain range to protect equipment and ensure normal system operation. Therefore, a well-designed circuit is required to achieve the transition between the tap changer's taps by properly controlling the on / off switching of each transition branch.

[0004] In existing technology, electromechanical hybrid power electronic on-load tap-changers are classified according to their thyristor triggering type: self-triggered thyristors and externally triggered thyristors. Self-triggered thyristors rely on the voltage difference and gate current generated by the arcing of the switch to trigger the thyristor, which carries a probability of triggering failure and is currently only suitable for voltage regulation in medium and low voltage distribution networks. Currently available externally triggered thyristors have complex topologies and response operations, resulting in lower reliability and are therefore unsuitable for ultra-high voltage transmission.

[0005] In the symmetrical four-thyristor assembly transition circuit currently widely used in the ultra-high voltage transmission field, the thyristor components realize different functions during switching, so their ablation degrees vary greatly, resulting in a significant reduction in the overall service life of the tap changer. Summary of the Invention

[0006] Based on the above-mentioned defects of the prior art, the present invention provides a power electronic on-load tap changer and a switching method thereof, which solves the problem that in the existing widely used symmetrical four-thyristor assembly transition circuit, the thyristor assemblies perform different functions during switching, resulting in greatly different degrees of ablation, which greatly reduces the overall service life of the tap changer.

[0007] The present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a power electronic on-load tap changer, comprising:

[0009] A first load branch includes a main pass-through switch M1 and a first switch branch connected in parallel with the main pass-through switch M1, wherein one end of the main pass-through switch M1 is connected to the transformer tap N and the other end is connected to the load; the first switch branch includes an isolating switch T1 and a thyristor assembly SCR1, wherein one end of the isolating switch T1 is connected to the load via the thyristor assembly SCR1 and the other end is switched between transformer taps N and N+1;

[0010] A second load branch includes a main pass-through switch M2 and a second switch branch connected in parallel with the main pass-through switch M2, wherein one end of the main pass-through switch M2 is connected to the transformer tap N+1 and the other end is connected to the load; the second switch branch includes an isolating switch T2 and a thyristor assembly SCR2, wherein one end of the isolating switch T2 is connected to the load via the thyristor assembly SCR2 and the other end is switched between transformer taps N and N+1;

[0011] The switching branch includes an isolating switch T3 and a thyristor assembly SCR3. One end of the isolating switch T3 is connected to the load through the thyristor assembly SCR3, and the other end switches between transformer taps N and N+1.

[0012] Preferably, when the other end of the isolating switch T1 switches between the transformer taps N and N+1, the isolating switch T1 is directly connected to the tap N, and the isolating switch T1 is connected to the tap N+1 via the resistor R1.

[0013] Preferably, when the other end of the isolating switch T2 switches between the transformer taps N and N+1, the isolating switch T2 is directly connected to the tap N+1, and the isolating switch T2 is connected to the tap N through the resistor R2.

[0014] In a second aspect, the present invention provides a switching method for a power electronic on-load tap changer, comprising the following steps:

[0015] When the load current of the transformer flows from tap N to the load, the load current supplies power to the load through the main pass-through switch M1. The first switch branch connects the transformer tap N, which is turned on by the main pass-through switch M1, to the load, and the switching branch disconnects the load. When the load current of the transformer flows from tap N+1 to the load, the load current supplies power to the load through the main pass-through switch M2. The second switch branch connects the transformer tap N+1, which is turned on by the main pass-through switch M2, to the load, and the switching branch disconnects the load.

[0016] When switching from transformer tap N to transformer tap N+1, the load current is switched from supplying the load through the main pass-through switch M1 to supplying the load through the main pass-through switch M2. The second switch branch connects the transformer tap N+1 (which is turned on by the main pass-through switch M2) to the load, and the switching branch is disconnected from the load.

[0017] When switching from transformer tap N+1 to transformer tap N, the load current is switched from supplying power to the load through the main pass-through switch M2 to supplying power to the load through the main pass-through switch M1. The first switch branch connects the transformer tap N, which is turned on by the main pass-through switch M1, to the load, and the switching branch disconnects the load.

[0018] Preferably, when switching from transformer tap N to transformer tap N+1, switching the load current from supplying power to the load through the main pass-through switch M1 to supplying power to the load through the main pass-through switch M2 comprises the following steps:

[0019] The main current-carrying switch M1 connected to the transformer tap N is disconnected, and the load current is supplied to the load through the switching branch;

[0020] The switching branch is disconnected, and the load current supplies power to the load through the second switching branch;

[0021] The switching branch is connected from transformer tap N to transformer tap N+1, and a circulating current is generated.

[0022] The second switch branch is disconnected, and the load current supplies power to the load through the switching branch;

[0023] The switching branch is disconnected from the transformer tap N+1, and the main current-carrying switch M2 is closed, completing the switching from the transformer tap N to the tap N+1.

[0024] Preferably, when switching from transformer tap N to transformer tap N+1, the load current is switched from supplying power to the load through the main pass-through switch M1 to supplying power to the load through the main pass-through switch M2, further comprising the following steps:

[0025] The main current-carrying switch M1 connected to the transformer tap N is disconnected, and the load current is supplied to the load through the switching branch;

[0026] The first switch branch is connected from transformer tap N to transformer tap N+1, generating a circulating current;

[0027] The switching branch is disconnected, and the load current supplies power to the load through the first switching branch;

[0028] The switching branch is connected to transformer tap N+1, and the load current is supplied to the load through the switching branch.

[0029] The switching branch is disconnected from the transformer tap N+1, and the load branch main current switch M2 is closed, completing the switching from the transformer tap N to the tap N+1.

[0030] Preferably, when switching from transformer tap N+1 to transformer tap N, switching the load current from supplying power to the load through the main pass-through switch M2 to supplying power to the load through the main pass-through switch M1 comprises the following steps:

[0031] The main current-carrying switch M2 connected to the transformer tap N+1 is disconnected, and the load current is supplied to the load through the switching branch;

[0032] The second switch branch is turned on, generating a circulating current;

[0033] The switching branch is disconnected, and the load current supplies power to the load through the second switching branch;

[0034] The switching branch is connected to the transformer tap N+1 and the second switching branch is disconnected, and the load current is supplied to the load through the switching branch;

[0035] The switching branch is disconnected from the transformer tap N+1, and the main current-carrying switch M1 is closed, completing the switching from the transformer tap N+1 to the tap N.

[0036] Preferably, when switching from transformer tap N+1 to transformer tap N, the load current is switched from supplying power to the load through the main pass-through switch M2 to supplying power to the load through the main pass-through switch M1, further comprising the following steps:

[0037] The main current-carrying switch M2 connected to the transformer tap N+1 is disconnected, and the load current is supplied to the load through the switching branch;

[0038] Connect the first switch branch from transformer tap N to transformer tap N+1, disconnect the switch branch, and supply the load current to the load through the first switch branch;

[0039] The switching branch is connected from transformer tap N+1 to transformer tap N, and a circulating current is generated.

[0040] The first switch branch is disconnected, and the load current supplies power to the load through the switching branch;

[0041] The switching branch is disconnected from the transformer tap N, and the main current-carrying switch M1 is closed, completing the switching from the transformer tap N+1 to the tap N.

[0042] Compared with the prior art, the at least one technical solution adopted by the present invention can achieve the following beneficial effects:

[0043] A power electronic on-load tap changer of the present invention includes a first load branch and a second load branch with a symmetrical structure. Each load branch includes a main current-passing switch and a switch branch connected in parallel with the main current-passing switch. Each switch circuit includes a thyristor assembly and an isolating switch. This redundant design reduces the electrical load borne by a single thyristor assembly and increases topological reliability.

[0044] The present invention also designs a switching method based on the switch design, which ensures that each switching can be completed safely and stably using one load branch and one switching branch. The two thyristors in the two load branches operate alternately during the switching process, thereby ensuring that the two thyristors have a relatively balanced degree of ablation, thereby improving the service life of the tap changer. At the same time, each thyristor component achieves zero current conduction or shutdown at the time of conduction or shutdown, thereby improving the service life and reliability of the tap changer and reducing the electrical tasks of each thyristor component. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 A topological diagram of a power electronic on-load tap changer according to the present invention;

[0047] Figure 2 A topological diagram of each step of the first sequential switching method during the switching of the tap changer from tap N to tap N+1 according to the present invention;

[0048] in, Figure 2 (a): Switch the topology diagram of step 1, Figure 2 (b): Switching topology diagram of step 2, Figure 2 (c): Switch to the topology diagram of step 3. Figure 2 (d): Switch to the topology diagram of step 4, Figure 2 (e): Switch to the topology diagram of step 5, Figure 2 (f): Switch to the topology diagram of step six, Figure 2 (g): topology diagram of switching step seven;

[0049] Figure 3 A timing diagram of a first switching method for switching the tap changer from tap N to tap N+1 according to the present invention;

[0050] in, Figure 3 (a): Timing diagram of switching step 1, Figure 3 (b): Timing diagram of switching step 2, Figure 3 (c): Timing diagram of switching step three, Figure 3 (d): Timing diagram of switching step four, Figure 3 (e): Timing diagram of switching step five, Figure 3 (f): Timing diagram of switching step six;

[0051] Figure 4 A topological diagram of each step of the first sequential switching method during the switching of the tap changer from tap N+1 to tap N of the present invention;

[0052] in, Figure 4 (a): Switch the topology diagram of step 1, Figure 4 (b): Switching topology diagram of step 2, Figure 4 (c): Switch to the topology diagram of step 3. Figure 4 (d): Switch to the topology diagram of step 4, Figure 4 (e): Switch to the topology diagram of step 5, Figure 4 (f): Switch to the topology diagram of step six, Figure 4 (g): topology diagram of switching step seven;

[0053] Figure 5 A timing diagram of a first switching method for switching the tap changer from tap N+1 to tap N according to the present invention;

[0054] in, Figure 5 (a): Timing diagram of switching step 1, Figure 5 (b): Timing diagram of switching step 2, Figure 5 (c): Timing diagram of switching step three, Figure 5 (d): Timing diagram of switching step four, Figure 5 (e): Timing diagram of switching step five, Figure 5 (f): Timing diagram of switching step six;

[0055] Figure 6 A topological diagram of each step of the second sequential switching method during the period when the tap changer switches from tap N to tap N+1 according to the present invention;

[0056] in, Figure 6 (a): Switch the topology diagram of step 1, Figure 6 (b): Switching topology diagram of step 2, Figure 6 (c): Switch to the topology diagram of step 3. Figure 6 (d): Switch to the topology diagram of step 4, Figure 6 (e): Switch to the topology diagram of step 5, Figure 6 (f): Switch to the topology diagram of step six, Figure 6 (g): Switch to the topology diagram of step seven, Figure 6 (h): topology diagram of switching step eight;

[0057] Figure 7 A timing diagram of a second switching method for switching the tap changer from tap N to tap N+1 according to the present invention;

[0058] in, Figure 7 (a): Timing diagram of switching step 1, Figure 7 (b): Timing diagram of switching step 2, Figure 7 (c): Timing diagram of switching step three, Figure 7 (d): Timing diagram of switching step four, Figure 7 (e): Timing diagram of switching step five, Figure 7 (f): Timing diagram of switching step six;

[0059] Figure 8 A topological diagram of each step of the second sequential switching method during the switching of the tap changer from tap N+1 to tap N of the present invention;

[0060] in, Figure 8 (a): Switch the topology diagram of step 1, Figure 8 (b): Switching topology diagram of step 2, Figure 8 (c): Switch to the topology diagram of step 3. Figure 8 (d): Switch to the topology diagram of step 4, Figure 8 (e): Switch to the topology diagram of step 5, Figure 8 (f): Switch to the topology diagram of step six, Figure 8 (g): Switch to the topology diagram of step seven, Figure 8 (h): topology diagram of switching step eight;

[0061] Figure 9 A timing diagram of a second switching method for switching the tap changer from tap N+1 to tap N according to the present invention;

[0062] in, Figure 9(a): Timing diagram of switching step 1, Figure 9 (b): Timing diagram of switching step 2, Figure 9 (c): Timing diagram of switching step three, Figure 9 (d): Timing diagram of switching step four, Figure 9 (e): Timing diagram of switching step five, Figure 9 (f) : Timing diagram of switching step six. DETAILED DESCRIPTION

[0063] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0064] like Figure 1 As shown, the present invention is a zero-current switching on-load tap changer based on a three-branch star-parallel structure. Each phase transition circuit includes three anti-parallel thyristor switch units SCR1, SCR2 and SCR3, three isolation switches T1, T2 and T3, two transition resistors R1 and R2 and two main current switches M1 and M2. Terminal N and terminal N+1 represent the transformer tap to be switched.

[0065] Main pass-through switch M1 is connected between tap N and the load, while main pass-through switch M2 is connected between tap N+1 and the load. Isolating switch T1 has one end connected to thyristor assembly SCR1 and the other end switched between tap N and transition resistor R1. The other end of transition resistor R1 is connected to tap N+1. Thyristor assembly SCR1 has one end connected to isolating switch T1 and the other end connected to the load.

[0066] One end of the isolating switch T2 is connected to the thyristor assembly SCR2, and the other end switches between the N+1 tap and the transition resistor R2, and the other end of the transition resistor R2 is connected to the tap N; one end of the thyristor assembly SCR2 is connected to the isolating switch T2, and the other end is connected to the load; one end of the isolating switch T3 is connected to the load through the thyristor assembly SCR3, and the other end switches between the tap N+1 and the tap N.

[0067] During normal operation, the load current supplies power to the load through the main pass switches. The two main pass switches are connected in parallel with two switch branches consisting of thyristor components and isolation switches, and fault tolerance is set for the main pass switches.

[0068] exist Figure 2 (a)- Figure 2(g) shows the various steps of switching the tap changer from tap N to tap N+1 according to the present invention, Figure 3 and Figure 5 The switching timing diagram corresponding to the switching process is shown in FIG. Figure 3 The first timing diagram representing the switching of tap N to N+1, Figure 5 The first timing diagram represents the switching of tap N+1 to N.

[0069] The following is a detailed description of the switching process:

[0070] See also Figure 2 (a) and Figure 3 , the main pass-through switch M1 of tap N is closed, the main pass-through switch M2 of tap N+1 is opened, and at the same time, disconnector T1 is connected to tap N, disconnector T2 is connected to transition resistor R2, and disconnector T3 is connected to tap N. The current of tap N flows to load O through the main pass-through switch M1.

[0071] See also Figure 2 (b) and Figure 3 , the main pass-through switch M1 is disconnected, triggering the thyristor assembly SCR3. At this point, SCR3 short-circuits the main pass-through switch M1 to prevent arcing. Disconnector T1 is connected to the N tap, disconnector T2 is connected to the transition resistor R2, and disconnector T3 is connected to the N tap. The current in the N tap flows through disconnector T3 and the thyristor assembly SCR3 to the load O. Switching to the other tap begins.

[0072] See also Figure 2 (c) and Figure 3 , the thyristor assembly SCR3 is turned off, the thyristor assembly SCR2 is triggered to turn on, the isolating switch T1 is connected to the tap N, the isolating switch T2 is connected to the transition resistor R2, and the isolating switch T3 is connected to the tap N. The current of the tap N flows to the load O through the thyristor assembly SCR2, the isolating switch T2 and the transition resistor R2.

[0073] See also Figure 2 (d) and Figure 3 Disconnector T3 switches to connect to tap N+1. Thyristor assembly SCR2 remains on, disconnector T1 connects to tap N, disconnector T2 connects to transition resistor R2, and disconnector T3 connects to tap N+1. The current in tap N flows to load O through thyristor assembly SR2, disconnector T2, and transition resistor R2.

[0074] See also Figure 2 (e) and Figure 3Thyristor assembly SCR2 remains on, triggering thyristor assembly SCR3. Isolator T1 is connected to tap N, Isolator T2 is connected to transition resistor R2, and Isolator T3 is connected to tap N+1. The current between taps N and N+1 flows through thyristor assembly SCR2, thyristor assembly SCR3, Isolator T2, Isolator T3, and transition resistor R2 to load O.

[0075] See also Figure 2 (f) and Figure 3 , disconnecting thyristor assembly SCR2, cutting off the circulating current. At this point, thyristor assembly SCR3 remains on, with disconnector T1 connected to tap N, disconnector T2 connected to transition resistor R2, and disconnector T3 connected to tap N+1. The current between taps N and N+1 flows through thyristor assembly SCR1, thyristor assembly SCR2, disconnector T1, disconnector T2, and transition resistors R1 and R2 to load O.

[0076] See also Figure 2 (g) and Figure 3 Close main pass-current switch M2. Thyristor assembly SCR3 short-circuits main pass-current switch M2, preventing arcing. Thyristor assembly SCR3 is turned off. The current in tap N+1 flows through main pass-current switch M2 to load O. The transfer ends at this step.

[0077] exist Figure 5 FIG. 2 shows a switching timing diagram of the tap changer according to the present invention when switching from the N+1 tap to the N tap. Figure 4 (a)- Figure 4 (g) The switching process from N+1 tap to N tap is similar in principle and process to the switching process from N tap to N+1 tap, and thus will not be described in detail here.

[0078] Figure 6 (a)- Figure 6 (h), Figure 7 , Figure 8 (a)- Figure 8 (h) and Figure 9 Another switch on-off timing diagram for switching from an N tap to an N+1 tap according to the present invention is shown, and the switch on-off timing diagram for switching from an N+1 tap to an N tap is shown. The processes are similar and will not be described in detail.

[0079] From the perspective of topological structure, in the traditional on-load tap changer circuit topology, the functions implemented by the thyristor components are not equal, resulting in severe ablation of the thyristor components during the switching process. The circuit topology provided by the present invention has two switching tubes operating alternately in two different timings, thereby ensuring that the two switching tubes have a relatively balanced ablation degree and improving the service life of the tap changer.

[0080] In terms of topology, each phase transition circuit of the tap changer of the present invention comprises two load branches and one switching branch. Each switching process requires only one load branch and one switching branch. This redundant design reduces the electrical load borne by a single thyristor assembly. Furthermore, the two transition resistors rotate between two different load branches, minimizing heat loss from a single transition resistor. This improves the reliability and robustness of system operation, making the tap changer safer and more reliable.

[0081] From the perspective of topological structure, the tap changer of the present invention has a relatively simple mechanical structure. At the same time, the electrical load of a single thyristor assembly and the heat generated by a single transition resistor are reduced, thereby achieving a balanced design of mechanical and electrical loads.

[0082] Control is born from topology. From a control perspective, the tap changer topology of this invention incorporates two different timing control strategies to achieve short circulation times and low heat losses. Each thyristor assembly achieves zero-current conduction and shutdown during the switching process, ensuring reliable on-load tap changer switching. This tap changer topology also offers fast switching speeds, with the entire switching process taking only 50ms, providing a certain degree of fault tolerance.

[0083] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0084] Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A switching method based on a power electronic on-load tap changer, characterized in that: The power electronic on-load tap changer comprises: The first load branch includes a main pass-through switch M 1 and the main current switch M 1 first switch branch in parallel, the main flow switch M 1 One end and transformer tap N The first switch branch includes an isolating switch T 1 and thyristor components SCR 1. The isolating switch T 1 One end passes through the thyristor assembly SCR 1 is connected to the load, and the other end is connected to the transformer tap N and N +1 switch between; Second load branch, including main pass switch M 2 and main flow switch M 2 parallel second switch branch, the main flow switch M 2 One end and transformer tap N +1 is connected, and the other end is connected to the load; the second switch branch includes an isolating switch T 2 and thyristor components SCR 2. The isolating switch T 2 One end passes through the thyristor assembly SCR 2 is connected to the load, and the other end is connected to the transformer tap N Switch between N+1; Switching branches, including disconnectors T 3 and thyristor components SCR 3. Isolating switch T 3 One end passes through the thyristor assembly SCR 3 is connected to the load, and the other end is connected to the transformer tap N and N +1 switch between; The switching method comprises the following steps: When the transformer load current is N When flowing into the load, the load current flows through the main current switch M 1 supplies power to the load, the first switch branch switches the main current M 1 conducting transformer tap N Connected to the load, the switching branch is disconnected from the load; when the load current of the transformer is N When +1 flows into the load, the load current flows through the main current switch M 2 supplies power to the load, and the second switch branch switches the main current flow switch M 2-conducting transformer taps N +1 is connected to the load, and the switching branch is disconnected from the load; When the transformer tap N Transformer tap N +1 switches, directing the load current through the main pass switch M 1. The power supply to the load is switched through the main current switch M 2 supplies power to the load, and the second switch branch switches the main current flow switch M 2-conducting transformer taps N +1 is connected to the load, and the switching branch is disconnected from the load; When the transformer tap N +1-way transformer tap N When switching, the load current is passed through the main current switch M 2. The load power supply is switched to the main current-carrying switch M 1 supplies power to the load, the first switch branch switches the main current M 1 conducting transformer tap N Connected to the load, the switching branch is disconnected from the load; When the transformer tap N Transformer tap N +1 switches, directing the load current through the main pass switch M 1. The power supply to the load is switched through the main current switch M 2. Supplying power to the load includes the following steps: Will be connected to the transformer tap N Main pass-through switch connected M 1 is disconnected, and the load current is supplied to the load through the switching branch; Connect the first switch branch to the transformer tap N Convert to transformer tap N +1 is connected, and a circulation is generated at this time; The switching branch is disconnected, and the load current supplies power to the load through the first switching branch; Switching branch transformer tap N Convert to transformer tap N +1 is connected, and the load current is supplied to the load through the switching branch; Switching branches and transformer taps N +1 is disconnected, the load branch main current switch M 2 Close, complete the transformer tap N Towards tap N +1 for switching.

2. A switching method based on a power electronic on-load tap changer according to claim 1, characterized in that: The isolating switch T 1 The other end is at the transformer tap N and N +1 when switching between the isolating switch T 1 Direct with tap N Connection, disconnect switch T 1 through the resistor R 1 with tap N +1 for connecting.

3. The switching method based on a power electronic on-load tap changer according to claim 1, characterized in that: The isolating switch T 2 The other end is at the transformer tap N and N +1 when switching between the isolating switch T 2 Direct and tap N +1 connection, isolating switch T 2 through the resistor R 2 with tap N connect.

4. The switching method based on a power electronic on-load tap changer according to claim 1, characterized in that: When the transformer tap N Transformer tap N +1 switches, directing the load current through the main pass switch M 1. The power supply to the load is switched through the main current switch M 2. Supplying power to the load further includes the following steps: Will be connected to the transformer tap N Main pass-through switch connected M 1 is disconnected, and the load current is supplied to the load through the switching branch; The switching branch is disconnected, and the load current supplies power to the load through the second switching branch; Switching branch transformer tap N Convert to transformer tap N +1 is connected, and a circulation is generated at this time; The second switch branch is disconnected, and the load current supplies power to the load through the switching branch; Switching branches and transformer taps N +1 disconnected, main flow switch M 2 Close, complete the transformer tap N Towards tap N +1 for switching.

5. The switching method based on a power electronic on-load tap changer according to claim 1, characterized in that: When the transformer tap N +1-way transformer tap N When switching, the load current is passed through the main current switch M 2. The load power supply is switched to the main current-carrying switch M 1 Supplying power to the load includes the following steps: Will be connected to the transformer tap N +1 connected mains pass-through switch M 2 is disconnected, and the load current supplies power to the load through the switching branch; The second switch branch is turned on, generating a circulating current; The switching branch is disconnected, and the load current supplies power to the load through the second switching branch; Switching branch transformer tap N +1 turns to the transformer tap N The second switch branch is disconnected, and the load current supplies power to the load through the switching branch; Switching branches and transformer taps N +1 disconnected, main flow switch M 1 Close, complete the transformer tap N +1-way tap N Switch.

6. The switching method based on a power electronic on-load tap changer according to claim 1, characterized in that: When the transformer tap N +1-way transformer tap N When switching, the load current is passed through the main current switch M 2. The load power supply is switched to the main current-carrying switch M 1. Supplying power to the load further includes the following steps: Will be connected to the transformer tap N +1 connected mains pass-through switch M 2 is disconnected, and the load current supplies power to the load through the switching branch; Connect the first switch branch to the transformer tap N Convert to transformer tap N +1 is connected, the switching branch is disconnected, and the load current supplies power to the load through the first switch branch; Switching branch transformer tap N +1 turns to the transformer tap N Connected, a circulation is generated at this time; The first switch branch is disconnected, and the load current supplies power to the load through the switching branch; Switching branches and transformer taps N Open, main current switch M 1 Close, complete the transformer tap N +1-way tap N Switch.

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