Three-level thin film capacitor and manufacturing process thereof

Abstract

The invention relates to the technical field of thin-film capacitors, in particular to a three-level thin-film capacitor and a manufacturing process thereof, which not only can meet the requirement of high capacity required in a high-power inverter, but also can reduce space occupation in an inverter module and facilitate installation, and comprises a capacitor shell and a capacitor core, the capacitor core comprises three core groups which are arranged in the same capacitor shell, each core group is composed of two groups of cores which are connected in parallel, two ends of each core group are fixedly connected with welding copper plates, the welding copper plates are connected with busbars provided with electrode through holes, extraction electrodes penetrate through the electrode through holes, and the extraction electrodes are connected with the busbars. The core is a flat core formed by winding a metalized film.

Description

Technical Field

[0001] The present invention relates to the technical field of film capacitors, and in particular to a three-level film capacitor and a manufacturing process thereof. Background Art

[0002] Metallized film capacitors have the characteristics of high voltage resistance, high ripple current bearing capacity, low ESR and ESL, etc. Metallized film capacitors are needed in the DC link of energy inverters to store energy and suppress ripple voltage to meet the normal operation of the inverter. However, with the emergence of high-voltage and high-current IGBT devices, three-level inverters have become a development direction for high-voltage and high-power inverters. Usually, film capacitors have small capacity, and multiple groups of film capacitors need to be connected in parallel in the inverter module, which causes inconvenience in installation and use. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a three-level film capacitor, which can not only meet the large capacity requirement of a high-power inverter, but also reduce the space occupied in the inverter module and facilitate installation.

[0004] The technical solution is as follows: a three-level film capacitor, which includes a capacitor housing and a capacitor core, characterized in that the capacitor core includes three core groups and is installed in the same capacitor housing, each of the core groups is composed of two groups of parallel cores and the two ends are fixedly connected to welded copper plates, the welded copper plates are connected to a busbar with electrode through holes, the lead electrodes pass through the electrode through holes, and the core is wound into a flat core by a metallized film.

[0005] It is further characterized in that the capacitor housing is an aluminum housing, the inner wall of the aluminum housing is polished and roughened and reinforced ribs are arranged at intervals; An insulating packaging cover plate is arranged on the glue-filling surface; The packaging insulation cover plate is provided with a glue injection port and a boss; The welding copper plate is provided with a glue through hole; A semi-T two-stage safety film structure is provided on the metallized film; The width of the transparent white stripes on both sides of the metallized film is reduced to 0.2 mm.

[0006] After adopting the present invention, three core groups are integrated into a capacitor housing, replacing the structure of connecting multiple three-level film capacitors in parallel, reducing the space occupancy rate, and being more convenient to install and use. In addition, the flat core structure has a higher energy density than a round core body, occupies a relatively small space, makes the internal space more compact, reduces the volume, and saves space. Each core group is composed of two groups of parallel cores, narrows the film width, increases the overcurrent capacity, and better meets the large capacity requirements of high-power inverters as a whole. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 A schematic diagram of a three-level film capacitor integrated group designed for the present invention; Figure 2 The internal structure diagram of the three-level film capacitor designed for the present invention; Figure 3 An exploded view of a three-level film capacitor designed for the present invention; Figure 4 It is a schematic diagram of the core structure; Figure 5 is a schematic diagram of a packaging cover; Figure 6 is a schematic diagram of the shell; Figure 7 This is a schematic diagram of welding copper plates; Figure 8 This is a schematic diagram of the connection between the conventional lead-out electrode and the busbar; Fig. 9 This is the schematic diagram of the connection between the electrode and the busbar for this design; Fig.10 It is a schematic diagram of the connection between the capacitor core and the welded copper plate; Fig.11 It is a schematic diagram of the assembly of the core, welding copper plate, electrode and shell; Fig.12 Schematic diagram of the metallized film structure. DETAILED DESCRIPTION

[0008] See Figures 1 to 12As shown, a three-level film capacitor includes a capacitor housing 1 and a capacitor core 3. The capacitor core 3 includes three core groups and is installed in the same capacitor housing 1. Each core group consists of two groups of cores 31 and 32 connected in parallel and the two ends are fixedly connected to a welded copper plate 4. Since the overcurrent capacity of the capacitor is related to the width and thickness of the metallized film, the narrower the metallized film, the stronger its current carrying capacity and the better its heat dissipation capacity. Therefore, in the present invention, the film width is narrowed, and two groups are connected in parallel to increase the overcurrent capacity. The welded copper plate 4 is connected to the electrode through hole. The busbar 5 is provided with welding pins 41 and glue through holes 42 on the welding copper plate. The glue through holes 42 facilitate the penetration of glue during glue filling to ensure that the glue filling of the product is sufficient. The lead-out electrode 6 passes through the electrode through hole. Since it is a three-level device, there are three lead-out electrodes. A laminated busbar is adopted, in which two electrodes pass through the through holes of the top busbar 5 without contacting each other. A cross-shaped bracket is provided at the bottom of the other electrode. After passing through the through hole, the cross-shaped bracket is used to support and weld the electrode. The busbar is clamped with a cross for welding from bottom to top to increase the welding firmness and prevent excessive force. Figure 8 The problem of electrode falling off in the existing structure shown.

[0009] Conventional capacitors use a round core structure design, which has the disadvantage of occupying a large space. As the market changes, there is an increasing demand for small and exquisite products. Therefore, the present invention uses a flat core wound by a metallized film to replace the round core. Compared with the round core, the flat core has a higher energy density and occupies a relatively small space, making the internal space more compact, reducing the volume, and saving space.

[0010] The capacitor housing 1 is an aluminum housing. Compared with other metals, aluminum has better heat dissipation performance. However, due to the presence of grease, dust, or too smooth surface on the metal surface, the metal surface becomes a weak interface layer, which will affect the adhesion of the resin. Therefore, the present invention performs a layer of grinding on the inner surface of the housing to increase the roughness of the inner surface, and at the same time adds several reinforcing ribs 11 on the inner surface to further increase the adhesion between the resin and the housing to prevent the plastic housing from detaching; in addition, the outer surface of the aluminum housing is sandblasted to prevent the housing from being corroded when the capacitor is used outdoors for a long time under high temperature and high humidity conditions.

[0011] Conventional capacitors are directly encapsulated with epoxy resin on the surface. Once the area of ​​the glue filling surface is large, the glue filling surface is prone to cracking after long-term use. The present invention adds an encapsulation cover plate 2 to the glue filling surface to prevent the glue filling surface from being too large, which causes the glue filling surface to crack. At the same time, the cover plate is made of insulating plastic material to increase the insulation performance between the lead-out electrode and the shell.

[0012] The package insulating cover plate is provided with a glue injection port 22 and a boss 21. The boss 21 can increase the creepage distance between the lead electrodes 6 and between the lead electrodes and the capacitor housing 1, thereby improving the insulation withstand voltage.

[0013] The film is made of 125℃ high temperature resistant polypropylene film, which has low tensile strength, elongation at break and thermal shrinkage, and exhibits excellent resistance to high temperature deformation. These characteristics ensure that the capacitor can continue to operate stably under high temperature conditions of 110℃ without performance degradation. In the design of the film coating, a semi-T two-stage edge thickening structure design is adopted. The conventional semi-T metallized safety film usually adopts a whole-stage design, which is easy to cause a large metal area failure, resulting in rapid capacity decay or even disappearance. Therefore, in the present invention, the conventional whole-stage design is modified to a two-stage design, that is, a metallized safety film with a semi-T two-stage structure. The film coating adopts a semi-ladder two-stage safety film explosion-proof structure 301, and the metal contact area of ​​the two sections, as well as the second section of the transverse fuse, can play a role in withstand voltage overload disconnection. And the width of the transparent white strips on both sides of the metallized film is reduced from 0.4mm to 0.2mm, which increases the contact area of ​​the metal coating, increases the effective capacity of the core, and reduces the outer diameter of the core. The introduction of the two-stage design not only enhances the explosion-proof effect of the safety film, but also significantly improves the overcurrent capacity of the capacitor core through the half-T edge thickened coating design, so that the capacitor can still maintain stable performance under harsh working conditions. The capacitor core is wound with a safe and high-temperature resistant metallized polypropylene film with a half-ladder two-stage structure. The capacitor core provided by the present invention is wound with a metallized polypropylene film with a half-ladder two-stage structure, has excellent high-temperature stability, high capacity, miniaturization, and enhanced explosion-proof and overcurrent capabilities, and is an ideal choice for capacitor manufacturing in high-temperature environments.

[0014] The present invention can not only meet the requirement of large capacity in a high-power inverter, but also reduce the space occupied in the inverter module and the problem of inconvenient installation.

[0015] At the same time, a specific manufacturing process is given for the above structure. Compared with the conventional capacitor structure, its manufacturing process improves the safety and reliability of the capacitor to a certain extent, while improving the automation capability, reducing costs and saving time. The specific process steps are as follows: The first step is to design a special copper plate that can connect multiple capacitor cores in parallel. Multiple welding points are set on this copper plate, which act as "bridges" connecting the capacitor cores. Then, using automated welding technology, the capacitor cores are precisely welded to these welding points, forming a collection of capacitor units, which we call a "core group."

[0016] The second step is to select two such core groups and connect them together through a conductive connecting bar, the "busbar", to build a capacitor integrated unit with three levels (i.e. three different voltage states). This three-level design can make the capacitor more stable and more efficient during operation.

[0017] The third step is to put three sets of such three-level capacitor integrated units into a solid housing and use potting material to completely wrap them for potting and encapsulation. This not only protects the capacitors from external environmental interference such as dust and moisture, but also helps the capacitors dissipate heat better and prolong their service life.

[0018] In summary, through these three key steps, the manufacturing process design of the integrated group of three-level film capacitors was successfully completed. The whole process is both delicate and scientific, ensuring the quality and performance of the final product.

Claims

1. A three-level film capacitor, comprising a capacitor housing and a capacitor core, characterized in that: The capacitor core includes three core groups and are installed in the same capacitor housing. Each core group consists of two groups of parallel cores and both ends are fixedly connected to welded copper plates. The welded copper plates are connected to a busbar with electrode through holes. The lead-out electrodes pass through the electrode through holes. The core is wound into a flat core by a metallized film. The capacitor housing is an aluminum shell. The inner wall of the aluminum shell is roughened and reinforced ribs are arranged at intervals. An insulating packaging cover is arranged on the glue-filled surface.

2. A three-level film capacitor according to claim 1, characterized in that: The packaging insulation cover plate is provided with a glue injection port and a boss.

3. The three-level film capacitor according to claim 1, characterized in that: The welding copper plate is provided with a glue through hole.

4. The three-level film capacitor according to claim 1, characterized in that: A semi-T two-stage safety film structure is arranged on the metallized film.

5. The three-level film capacitor according to claim 1, characterized in that: The width of the transparent white stripes on both sides of the metallized film is reduced to 0.2 mm.

6. A three-level film capacitor and its manufacturing process, characterized in that: It includes the following steps: (1) Multiple welding points are set on the copper plate, and the capacitor core is accurately welded to these welding points using automated welding technology, thereby forming a collection of capacitor units to form a core group; (2) Select two groups of core groups in step (1), connect them together through busbars, and construct a capacitor integrated unit with three levels; (3) Place the three groups of three-level capacitor integrated units in step (2) into a sturdy housing and completely wrap them with a potting material for potting and packaging.

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