Isolation transformer, converter and circuit thereof

Abstract

The utility model relates to the technical field of power conversion, and discloses an isolation transformer, a converter and a circuit thereof. The isolation transformer comprises a framework, an iron core, a primary winding and a secondary winding, two primary winding ports are formed in one side of the framework, three secondary winding ports are formed in the other side of the framework, and the secondary winding ports comprise a center winding port. A neutral line is formed on the secondary side of the isolation transformer, the neutral line enables two groups of voltage outputs of the secondary side of the transformer to be consistent, the neutral line of the isolation transformer is connected with the neutral point of a direct-current bus of an inversion module of the converter, the neutral point balance of the direct-current bus of the inversion module of the converter is guaranteed, and all switching devices are ensured to work under the same voltage. Therefore, the power system can operate stably, loss can be reduced, and overall efficiency is improved.

Description

Technical Field

[0001] The present application relates to the technical field of power conversion, and in particular to an isolation transformer, a converter and a circuit thereof. Background Art

[0002] In rail transit systems, vehicles require electricity to drive their operation. The power supply network may provide direct current, and the heat dissipating traction motor needs to use alternating current to operate. Usually, an inverter is used to convert direct current into adjustable frequency alternating current to meet the needs of the motor.

[0003] The converter in the prior art uses a fully encapsulated high-frequency transformer for isolation. This high-frequency transformer requires the magnetic core and wires to be encapsulated with a metal shell and thermal conductive adhesive. The voltage fluctuation at the midpoint of the DC bus of the inverter module of the converter in the prior art is large, which interferes with the dynamic balance of the system, causes the control system to be unstable, and affects the stable operation of the entire power system. Utility Model Content

[0004] In view of this, the embodiments of the present application provide an isolation transformer, a converter and a circuit thereof, which can effectively solve the problem in the existing solution that the voltage fluctuation at the midpoint of the DC bus of the inverter module of the converter is large, which interferes with the dynamic balance of the system, causes the control system to be unstable, and affects the stable operation of the entire power system.

[0005] In a first aspect, an embodiment of the present application provides an isolation transformer, comprising: a frame, a primary winding and a secondary winding, wherein the primary winding and the secondary winding are both wound around the frame, the primary winding comprises a first winding coil, the secondary winding comprises a second winding coil and a third winding coil, the first winding coil comprises a first interlayer winding coil and a second interlayer winding coil, the first interlayer winding coil is arranged in an inner layer, the second interlayer winding coil is arranged in an outer layer, the second winding coil and the third winding coil are arranged between the first interlayer winding coil and the second interlayer winding coil as an intermediate layer winding of the isolation transformer;

[0006] A primary winding inlet port and a primary winding outlet port are arranged on one side of the frame, and three secondary winding ports are arranged on the other side of the frame, wherein the three secondary winding ports include a central winding port.

[0007] In some embodiments, the number of turns of the second winding coil is the same as the number of turns of the third winding coil, the second winding coil and the third winding coil are arranged in parallel, and the outlet end of the second winding coil and the inlet end of the third winding coil are arranged at the central winding port.

[0008] In some embodiments, the cables of the primary winding and the secondary winding are square Litz wires formed by twisting N Litz wires into a square, where N is a positive integer greater than 1.

[0009] In some embodiments, a high temperature resistant insulation layer is provided between the first interlayer winding coil and the frame, between the first interlayer winding coil, the middle layer winding and the second interlayer winding coil, and on the outer surface of the second interlayer winding coil.

[0010] In some embodiments, the high temperature resistant insulating layer is an insulating tape.

[0011] In some embodiments, retaining walls are provided at both ends of the winding coil between the high temperature resistant insulation layers.

[0012] In a second aspect, an embodiment of the present application provides a converter circuit, comprising: an input energy storage circuit, a three-phase series interleaved full-bridge resonant circuit, a three-phase parallel rectifier circuit, and a three-level inverter circuit;

[0013] The positive electrode of the input energy storage circuit is used to connect to the positive electrode of the power supply, the negative electrode of the input energy storage circuit is used to connect to the negative electrode of the power supply, the input end of the three-phase series interleaved full-bridge resonant circuit is electrically connected to the input energy storage circuit, the output end of the three-phase series interleaved full-bridge resonant circuit is electrically connected to the input end of the three-phase parallel rectifier circuit, the output end of the three-phase parallel rectifier circuit is electrically connected to the input end of the three-level inverter circuit, and the output end of the three-level inverter circuit is used to output a three-phase AC signal;

[0014] The three-phase series interleaved full-bridge resonant circuit includes three full-bridge resonant units, each of which includes a full-bridge switch group and a resonant cavity, and the resonant cavity includes at least one isolation transformer described in the first aspect, and the midpoint of the secondary output end of the isolation transformer is connected to the bus midpoint of the three-level inverter circuit.

[0015] In some embodiments, the input energy storage circuit includes three input capacitors, and the three input capacitors are sequentially connected in series between the positive electrode of the power supply and the negative electrode of the power supply.

[0016] In some embodiments, the converter circuit also includes: an input filter circuit and an output filter circuit, the input end of the input filter circuit is connected to the output end of the three-phase parallel rectifier circuit, the output end of the input filter circuit is electrically connected to the input end of the three-level inverter circuit, the output filter circuit is connected to the output end of the three-level inverter circuit, and the output end of the output filter circuit is used to output the filtered three-phase AC signal.

[0017] In a third aspect, an embodiment of the present application provides a converter, comprising a housing and at least one converter circuit as described in the second aspect.

[0018] The embodiments of the present application have the following beneficial effects:

[0019] The isolation transformer of the present application includes: a skeleton, an iron core, a primary winding and a secondary winding. The coil of the primary winding is divided into two parts for winding. During winding, the incoming line end of the primary coil is wound flat on the skeleton, and a first interlayer winding is formed after winding a first preset number of turns. The second winding coil and the third winding coil are arranged on the same layer as an intermediate layer winding. The other part of the cable of the primary coil is wound above the intermediate layer winding to form a second interlayer winding. Two primary winding ports are arranged on one side of the skeleton, and three secondary winding ports are arranged on the other side of the skeleton. The secondary winding port includes a central winding port. The present application forms a neutral line on the secondary side of the isolation transformer by arranging a central winding port on the secondary port part on the isolation transformer. The neutral line makes the two sets of voltage outputs on the secondary side of the transformer consistent. The neutral line of the isolation transformer is connected to the midpoint of the DC bus of the inverter module of the converter to ensure the balance of the midpoint of the DC bus of the inverter module of the converter, and ensure that all switching devices work at the same voltage, so that the power system can operate stably, while reducing losses and improving overall efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A schematic diagram showing the principle of an isolation transformer according to an embodiment of the present application is shown;

[0022] Figure 2 A schematic diagram of the structure of the isolation transformer according to an embodiment of the present application is shown;

[0023] Figure 3 A front view of an isolation transformer according to an embodiment of the present application is shown;

[0024] Figure 4 A side view of an isolation transformer according to an embodiment of the present application is shown;

[0025] Figure 5 A bottom view of an isolation transformer according to an embodiment of the present application is shown;

[0026] Figure 6 A first structural schematic diagram of a converter circuit according to an embodiment of the present application is shown;

[0027] Figure 7 A circuit diagram of a high-voltage charger according to an embodiment of the present application is shown.

[0028] Description of main component symbols: 1: primary winding inlet port; 2: primary winding outlet port; 3: secondary winding outlet port; 4: secondary winding inlet port; 5: center winding port;

[0029] N1: first winding coil; N2: second winding coil; N3: third winding coil;

[0030] 11: skeleton; 12: iron core; 13: primary winding; 14: secondary winding; 15: square Litz wire; 16: insulating tape; 17: retaining wall; 21: power supply; 22: input energy storage circuit; 23: three-phase series interleaved full-bridge resonant circuit; 24: three-phase parallel rectifier circuit; 25: input filter circuit; 26: three-level inverter circuit; 27: output filter circuit; 28: isolation transformer. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0032] The components of the embodiments of the present application generally described and shown in the drawings herein may be arranged and designed in various configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0033] Hereinafter, the terms "including", "having" and their cognates that can be used in various embodiments of the present application are intended only to indicate specific features, numbers, steps, operations, elements, components or a combination of the foregoing items, and should not be understood as first excluding the existence of one or more other features, numbers, steps, operations, elements, components or a combination of the foregoing items or increasing the possibility of one or more features, numbers, steps, operations, elements, components or a combination of the foregoing items. In addition, the terms "first", "second", "third" and the like are only used to distinguish descriptions and cannot be understood as indicating or implying relative importance.

[0034] Unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meanings as those generally understood by those skilled in the art to which the various embodiments of the present application belong. The terms (such as those defined in generally used dictionaries) will be interpreted as having the same meanings as the contextual meanings in the relevant technical field and will not be interpreted as having idealized meanings or overly formal meanings unless clearly defined in the various embodiments of the present application.

[0035] In conjunction with the accompanying drawings, some embodiments of the present application are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0036] Taking into account the problem that the voltage fluctuation at the midpoint of the DC bus of the inverter module of the converter in the existing solution is large, which interferes with the dynamic balance of the system, causes instability in the control system, and affects the stable operation of the entire power system, the present application provides an isolation transformer, a converter and its circuit. The present application sets a central winding port on the secondary port part of the isolation transformer to form a neutral line on the secondary side of the isolation transformer. The neutral line makes the two sets of voltage outputs on the secondary side of the transformer consistent. The neutral line of the isolation transformer is connected to the midpoint of the DC bus of the inverter module of the converter to ensure the balance of the DC bus midpoint of the inverter module of the converter, ensure that all switching devices operate at the same voltage, so that the power system can operate stably, while reducing losses and improving overall efficiency.

[0037] The isolation transformer is described below in conjunction with some specific embodiments.

[0038] As an optional solution, Figure 1 The figure shows a schematic diagram of the principle of an isolation transformer. Figure 2 Shown Figure 1 The structural diagram of the isolation transformer, Figure 3 Shown Figure 1 Front view of the isolation transformer, Figure 4 Shown Figure 1 Side view of the isolation transformer, Figure 5 Shown Figure 1 Bottom view of the isolation transformer.

[0039] In one embodiment, if Figures 1 to 5As shown, the isolation transformer includes: a skeleton 11, an iron core 12, a primary winding 13 and a secondary winding 14, the primary winding 13 and the secondary winding 14 are both wound around the skeleton 11, the primary winding 13 includes a first winding coil N1, the secondary winding 14 includes a second winding coil N2 and a third winding coil N3, the first winding coil N1 includes a first interlayer winding coil and a second interlayer winding coil, the first interlayer winding coil is arranged in the inner layer, the second interlayer winding coil is arranged in the outer layer, the second winding coil N2 and the third winding coil N3 are arranged between the first interlayer winding coil and the second interlayer winding coil as the intermediate layer winding of the isolation transformer.

[0040] It can be understood that point P is the output end of the first interlayer winding coil, and the number of turns of each coil can be set according to the actual application situation. Exemplarily, the number of turns of the first interlayer winding coil is the same as the number of turns of the second interlayer winding coil, and the number of turns of the second winding coil N2 and the third winding coil N3 are the same.

[0041] A primary winding inlet port 1 and a primary winding outlet port 2 are provided on one side of the skeleton 11 , and three secondary winding 14 ports are provided on the other side of the skeleton 11 . The three secondary winding 14 ports include a central winding port 5 .

[0042] Specifically, the three secondary winding 14 ports also include a secondary winding input port 4, a secondary winding output port 3, the input end of the first winding coil N1 is set at the primary winding input port 1, the output end of the first winding coil N1 is set at the output port of the primary winding 13, the input end of the second winding coil N2 is set at the secondary winding input port 4, the output end of the second winding coil N2 is set at the center winding port 5, the input end of the third winding coil N3 is set at the center winding port 5, and the output end of the third winding coil N3 is set at the secondary winding output port 3.

[0043] The cable of the winding may be an enameled wire, a multi-strand wire, a three-layer insulated wire, a silk-covered wire, or a copper foil.

[0044] It is understandable that the cable is tightly wound during the winding process. If it cannot be wound in one layer, it needs to be evenly distributed, and the cable cannot be overlapped during the winding process.

[0045] Furthermore, the wound transformer is treated with varnish to further strengthen the insulation of the transformer.

[0046] The isolation transformer of this embodiment forms a neutral line on the secondary side of the isolation transformer by setting a central winding port 5 on the secondary port part of the isolation transformer. The neutral line makes the two sets of voltage outputs on the secondary side of the transformer consistent. The neutral line of the isolation transformer is connected to the midpoint of the DC bus of the inverter module of the converter, which suppresses the fluctuation of the midpoint voltage of the DC bus, keeps the midpoint voltage of the DC bus of the inverter module of the converter balanced, reduces the total harmonic distortion of the inverter output voltage, and greatly improves the quality of the signal.

[0047] In one embodiment, if Figures 1 to 5 As shown, based on the above embodiment, the number of turns of the second winding coil N2 is the same as the number of turns of the third winding coil N3, the second winding coil N2 and the third winding coil N3 are arranged in parallel, and the outlet end of the second winding coil N2 and the inlet end of the third winding coil N3 are arranged at the center winding port 5.

[0048] The isolation transformer of this embodiment makes the number of turns of the second winding coil N2 the same as the number of turns of the third winding coil N3 and winds the second winding coil N2 and the third winding coil N3 in parallel, so that the performance of the secondary winding 14 is consistent, the inductance of the two windings is ensured to be consistent, and the two sets of voltage outputs on the secondary side of the transformer are further ensured to be consistent.

[0049] In one embodiment, if Figures 1 to 5 As shown, based on the above embodiment, the cables of the primary winding and the secondary winding are square Litz wires 15 formed by twisting N Litz wires into a square shape.

[0050] Specifically, the square Litz wire 15 is formed by twisting N round Litz wires and then pressing them into a square shape. For example, the diameter of the round Litz wire is 0.05 mm, and the number of round Litz wires in the square Litz wire 15 is 800-1000. Furthermore, in order to meet safety requirements, the squared Litz wire can be wrapped with a high temperature resistant insulating tape 16 to ensure the insulation of the cable.

[0051] The isolation transformer of this embodiment sets the transformer cable as a square Litz wire 15. The twisted Litz wire can significantly reduce the skin effect and the proximity effect, thereby reducing the AC resistance at high frequencies and improving efficiency. The square Litz wires are tightly arranged in a limited space to achieve a miniaturized and lightweight design.

[0052] In one embodiment, if Figures 1 to 5 As shown, based on the above embodiment, a high temperature resistant insulation layer is arranged between the first interlayer winding coil and the skeleton 11, between the first interlayer winding coil, the middle layer winding and the second interlayer winding coil, and on the outer surface of the second interlayer winding coil.

[0053] Specifically, the high temperature resistant insulating layer may be mica, or the high temperature resistant insulating layer may be insulating tape 16. Exemplarily, the high temperature resistant insulating layer is insulating tape 16, and the number of layers of the high temperature resistant insulating layer may be set according to actual application conditions.

[0054] The isolation transformer of this embodiment is provided with a high-temperature resistant insulation layer between the first-layer winding coil and the skeleton 11. The high-temperature resistant insulation layer can withstand the high temperature generated by the transformer or motor during operation, prevent heat from being directly transferred to the skeleton 11, and protect the skeleton 11 material from thermal damage; the high-temperature resistant insulation layer is provided between layers to ensure electrical isolation between adjacent winding layers and between the winding and the iron core 12 or the casing, prevent short circuit or leakage, and ensure the electrical safety of the equipment.

[0055] In one embodiment, if Figures 1 to 5 As shown, based on the above embodiment, the high temperature resistant insulating layer is an insulating tape 16 .

[0056] Exemplarily, the insulating tape 16 is a polyimide insulating tape 16 , and the insulating tape 16 has three layers. The first layer can provide the most basic electrical isolation, the second layer can enhance mechanical strength and further electrical isolation, and the third layer can prevent damage to the insulating layer by the external environment.

[0057] In one embodiment, if Figures 1 to 5 As shown, based on the above embodiment, retaining walls are provided at both ends of the winding coil between the high temperature resistant insulation layers.

[0058] It is understood that the thickness of the retaining wall 17 of each layer is the same as the thickness of the winding coil. After the first interlayer winding coil is wound, an insulating tape 16 is set on the winding as needed, and a retaining wall 17 of the middle layer winding is set on the insulating tape 16. After the retaining wall 17 is set, the middle layer winding is wound, and the thickness of the retaining wall 17 can be set according to the actual application. It is understood that the cable cannot be wound on the retaining wall 17 during the winding process.

[0059] The isolation transformer of this embodiment is provided with retaining walls 17 between layers. The retaining walls 17 can increase the electrical isolation between winding layers, prevent interlayer short circuits caused by aging, moisture or overheating of the insulating material, greatly improve the insulation capacity of the transformer, and at the same time can provide additional mechanical support to maintain the structural stability of the winding.

[0060] As an optional solution, Figure 6 The figure shows a schematic diagram of a converter circuit. Figure 7 Shown Figure 6 A circuit diagram of a converter circuit.

[0061] In one embodiment, if Figure 6 and Figure 7As shown, the converter circuit includes: an input energy storage circuit 22 , a three-phase series interleaved full-bridge resonant circuit 23 , a three-phase parallel rectifier circuit 24 and a three-level inverter circuit 26 .

[0062] The positive electrode of the input energy storage circuit 22 is used to connect to the positive electrode of the power supply 21, and the negative electrode of the input energy storage circuit 22 is used to connect to the negative electrode of the power supply 21. It can be understood that multiple energy storage capacitors can be set in the input energy storage circuit 22 of this embodiment, and the input ends of the three-phase series interleaved full-bridge resonant circuit 23 can be connected in series using multiple energy storage capacitors.

[0063] The input end of the three-phase series interleaved full-bridge resonant circuit 23 is electrically connected to the input energy storage circuit 22, and the output end of the three-phase series interleaved full-bridge resonant circuit 23 is electrically connected to the input end of the three-phase parallel rectifier circuit 24. As an optional scheme, each full-bridge resonant circuit in the three-phase series interleaved full-bridge resonant circuit 23 is an LLC full-bridge resonant circuit, and the phase difference of each pulse signal of the three-phase series interleaved full-bridge resonant circuit 23 is 120 degrees.

[0064] The output end of the three-phase parallel rectifier circuit 24 is electrically connected to the input end of the three-level inverter circuit 26, and the output end of the three-level inverter circuit 26 is used to output a three-phase AC signal. Figure 7 As shown, each phase of the three-level inverter circuit 26 includes four switching tubes. It can be understood that the switching tubes in this embodiment can be any type of switching tubes, the switching tubes can be MOS tubes, and the switching tubes can also be field effect tubes. In the three-level inverter circuit 26, the full-bridge inverter circuits of each phase can be controlled separately, and the amplitude and frequency of the sinusoidal modulation signals of each phase between the three phases are the same, and the phase difference is 120 degrees. Each phase is modulated and the duty cycle is calculated based on the bus voltage, and the three-level inverter circuit 26 is controlled by a sinusoidal pulse width modulation method.

[0065] The three-phase series interleaved full-bridge resonant circuit 23 includes three full-bridge resonant units, each of which includes a full-bridge switch group and a resonant cavity. The resonant cavity includes the isolation transformer 28 mentioned in any of the above embodiments, and the midpoint of the secondary output end of the isolation transformer 28 is connected to the bus midpoint of the three-level inverter circuit 26.

[0066] It is understandable that the switches in the three-phase series resonant circuit and the three-level inverter circuit 26 should be electrically connected to the controller, and the controller is used to control the on and off of the switches in the three-phase series resonant circuit and the three-level inverter circuit 26.

[0067] The working process of the converter circuit of this embodiment is as follows: the power supply 21 charges the input energy storage circuit 22, and the controller can control the pulse signal of the three-phase series interleaved full-bridge resonant circuit 23 according to the resonance gain, and control the output voltage of the three-phase series interleaved full-bridge resonant circuit 23 by adjusting the frequency or phase of the pulse signal of the three-phase series interleaved full-bridge resonant circuit 23. The output voltage is rectified by the three-phase parallel rectifier circuit 24 and flows to the three-level inverter circuit 26 to provide stable power supply to the midpoint of the three-level inverter circuit 26. The duty cycle of each phase is modulated and calculated based on the bus voltage, and the controller uses a sinusoidal pulse width modulation method to control each item of the three-level inverter circuit 26 separately.

[0068] When the load connected to the output end of the three-level inverter circuit 26 is unbalanced, the voltage charging point at the midpoint of the DC bus is inconsistent, which interferes with the dynamic balance of the system and increases the harmonic content of the sinusoidal voltage output by the inverter circuit. The converter circuit of this embodiment makes the two sets of voltage outputs on the secondary side of the transformer consistent through the neutral line of the isolation transformer 28, suppresses the fluctuation of the midpoint voltage of the DC bus, reduces the total harmonic distortion of the inverter output voltage, and greatly improves the quality of the signal.

[0069] In one embodiment, if Figure 6 and Figure 7 As shown, based on the above embodiment, the input energy storage circuit 22 includes three input capacitors, and the three input capacitors are connected in series between the positive electrode of the power supply 21 and the negative electrode of the power supply 21. Preferably, the capacity of the three input capacitors is the same, which can ensure the balanced distribution of current in each phase of the three-phase circuit.

[0070] The converter circuit of this embodiment sets three input capacitors in the input energy storage circuit 22, and uses three capacitors with the same capacity to realize the input series connection of the three-phase series staggered full-bridge resonant circuit 23, which can ensure that the circuit works in a three-phase balanced state and improve the efficiency, stability and reliability of the circuit.

[0071] In one embodiment, if Figure 6 and Figure 7 As shown, based on the above embodiment, the converter circuit further includes: an input filter circuit 25 and an output filter circuit 27, the input end of the input filter circuit 25 is connected to the output end of the three-phase parallel rectifier circuit 24, the output end of the input filter circuit 25 is electrically connected to the input end of the three-level inverter circuit 26, the output filter circuit 27 is connected to the output end of the three-level inverter circuit 26, and the output end of the output filter circuit 27 is used to output the filtered three-phase AC signal.

[0072] It is understandable that the filter circuit of this embodiment can be any filter circuit. For example, a filter resistor and a filter capacitor can be set in the filter circuit to form an RC filter; a filter resistor and a filter inductor can be set in the filter circuit to form an RL filter; a filter inductor and a filter capacitor can be set in the filter circuit to form an LC filter; or a filter capacitor, a filter inductor and a filter resistor can be set in the filter circuit to form an RLC filter. For example, Figure 7 As shown, a filter capacitor and a filter resistor are provided in the input filter circuit 25 for filtering, and a filter inductor and a filter capacitor are provided in the output filter circuit 27 for filtering.

[0073] In the converter circuit of this embodiment, a filter capacitor and a filter resistor are set at the input end of the three-level inverter circuit 26 for filtering. The filter capacitor can be used as an energy buffer to absorb instantaneous overvoltage, smooth the voltage fluctuation in the circuit, and ensure that the inverter receives a stable DC voltage. At the same time, it can attenuate electromagnetic interference and reduce the interference of the inverter to surrounding electronic equipment; a filter inductor and a filter capacitor are set at the output end of the three-level inverter circuit 26 for filtering, which can improve the voltage and current waveforms of the inverter output, reduce high-frequency noise, and ensure that the output power quality meets specific application requirements.

[0074] An embodiment of the present application further provides a converter. Exemplarily, the converter includes the above converter circuit.

[0075] The above description is only a specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application.

Claims

1. An isolation transformer, characterized in that: include: A skeleton, a primary winding and a secondary winding, wherein the primary winding and the secondary winding are both wound around the skeleton, the primary winding comprises a first winding coil, the secondary winding comprises a second winding coil and a third winding coil, the first winding coil comprises a first interlayer winding coil and a second interlayer winding coil, the first interlayer winding coil is arranged on an inner layer, the second interlayer winding coil is arranged on an outer layer, the second winding coil and the third winding coil are arranged between the first interlayer winding coil and the second interlayer winding coil as an intermediate layer winding of the isolation transformer; A primary winding inlet port and a primary winding outlet port are arranged on one side of the frame, and three secondary winding ports are arranged on the other side of the frame, wherein the three secondary winding ports include a central winding port.

2. The isolation transformer according to claim 1, characterized in that: The number of turns of the second winding coil is the same as the number of turns of the third winding coil, the second winding coil and the third winding coil are arranged in parallel, and the outlet end of the second winding coil and the inlet end of the third winding coil are arranged at the central winding port.

3. The isolation transformer according to claim 1, characterized in that: The cables of the primary winding and the secondary winding are square Litz wires formed by twisting N Litz wires into a square, where N is a positive integer greater than 1.

4. The isolation transformer according to claim 1, characterized in that: A high temperature resistant insulating layer is arranged between the first interlayer winding coil and the frame, between the first interlayer winding coil, the middle layer winding and the second interlayer winding coil, and on the outer surface of the second interlayer winding coil.

5. The isolation transformer according to claim 4, characterized in that: The high temperature resistant insulating layer is an insulating tape.

6. The isolation transformer according to claim 4, characterized in that: Both ends of the winding coil between the high temperature resistant insulation layers are provided with retaining walls.

7. A converter circuit, characterized in that: include: Input energy storage circuit, three-phase series interleaved full-bridge resonant circuit, three-phase parallel rectifier circuit and three-level inverter circuit; The positive electrode of the input energy storage circuit is used to connect to the positive electrode of the power supply, the negative electrode of the input energy storage circuit is used to connect to the negative electrode of the power supply, the input end of the three-phase series interleaved full-bridge resonant circuit is electrically connected to the input energy storage circuit, the output end of the three-phase series interleaved full-bridge resonant circuit is electrically connected to the input end of the three-phase parallel rectifier circuit, the output end of the three-phase parallel rectifier circuit is electrically connected to the input end of the three-level inverter circuit, and the output end of the three-level inverter circuit is used to output a three-phase AC signal; The three-phase series interleaved full-bridge resonant circuit includes three full-bridge resonant units, each of which includes a full-bridge switch group and a resonant cavity, and the resonant cavity includes the isolation transformer as described in any one of claims 1-6, and the midpoint of the secondary output end of the isolation transformer is connected to the bus midpoint of the three-level inverter circuit.

8. The converter circuit according to claim 7, characterized in that: The input energy storage circuit includes three input capacitors, and the three input capacitors are sequentially connected in series between the positive electrode of the power supply and the negative electrode of the power supply.

9. The converter circuit according to claim 7, characterized in that: The converter circuit also includes: an input filter circuit and an output filter circuit, the input end of the input filter circuit is connected to the output end of the three-phase parallel rectifier circuit, the output end of the input filter circuit is electrically connected to the input end of the three-level inverter circuit, the output filter circuit is connected to the output end of the three-level inverter circuit, and the output end of the output filter circuit is used to output the filtered three-phase AC signal.

10. A converter, characterized in that: The converter comprises a housing and the converter circuit according to any one of claims 7 to 9.

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