Anti-electromagnetic interference filter for motor control

Abstract

The utility model discloses an anti-electromagnetic interference filter for motor control, which belongs to the technical field of anti-electromagnetic interference filters for motor control, and specifically structurally comprises a metal shell, a circuit board and a metal cover plate, the metal shell is provided with an accommodating cavity, the circuit board is mounted in the accommodating cavity, and five guide pins are arranged at the bottom of the circuit board, the four guide pins extend out of the bottom of the metal shell and are isolated from the bottom of the metal shell by adopting glass insulators, the four guide pins are respectively an input positive end, an input negative end, an output positive end and an output negative end, and the fifth guide pin is a grounding end and is fixedly connected to the bottom of the metal shell; the containing cavity is filled with pouring sealant after the circuit board is installed, and the bottom of the metal shell is connected to a grounding bonding pad on the circuit board. According to the filter, a multi-stage LC filter circuit is formed in a small enough space, high suppression capability is provided, and meanwhile, the filter is manufactured by metal packaging and can resist interference.

Description

Technical Field

[0001] This utility model relates to a filter for electromagnetic interference suppression in motor control, belonging to the field of filter technology. Background Technology

[0002] When a brushless motor starts up, the voltage overshoots and the magnetic field changes instantaneously, generating very strong current and electromagnetic fields, which can easily cause sparks. In addition, due to the insufficient precision between the rotor and stator of the brushless motor, weak contact or friction often occurs during operation due to rotational inertia and repeated switching of the magnetic field, which can also generate sparks. When the motor rotates at high speed, these sparks are conducted to the motor control system through the brushless motor power circuit, and coupled together with the interference generated by the switching of MOSFETs and diodes in the motor control system, and conducted out through the power interface of the motor control system, thereby interfering with the normal operation of other equipment.

[0003] Considering the operating characteristics of brushless motors and the transmission path of interference, for electromagnetic interference and its harmonic electromagnetic interference at rotational speeds of brushless motors as high as 20kHz-75kHz, a filter with high suppression capability needs to be installed before the power interface of the motor control system to suppress it, ensuring that it does not affect the normal operation of other equipment. The problem can be completely solved by using the filter to address the transmission path.

[0004] Typically, motor control system modules have limited space, and the space for installing filters is extremely limited. Only filters with a size of 51mm x 31mm or smaller can be installed. However, smaller filters often need to consider space utilization and circuit layout, and the suppression capability they can provide is poor. A single filter cannot solve the problem. Usually, two or even three filters with similar sizes need to be connected in series, which far exceeds the space required by the motor control system, making it impossible to implement. Utility Model Content

[0005] The technical problem to be solved by this utility model is to provide a filter for electromagnetic interference suppression in motor control, which provides high suppression capability, and the filter is made of metal packaging, so it can also resist interference itself.

[0006] The technical solution adopted by this utility model is as follows: a filter for electromagnetic interference suppression in motor control, comprising a metal shell, a circuit board, and a metal cover plate. The metal shell is provided with a receiving cavity with an opening at the top. The circuit board is installed in the receiving cavity, and the circuit components of the filter are installed on the circuit board. Five guide pins are provided at the bottom of the circuit board. Among them, four guide pins extend out of the bottom of the metal shell and are isolated from the bottom of the metal shell by glass insulators. The four guide pins are respectively the positive input terminal, the negative input terminal, the positive output terminal, and the negative output terminal. The fifth guide pin is the grounding terminal, which is fixedly connected to the bottom of the metal shell. The metal cover plate covers the opening of the metal shell. After the receiving cavity is installed with the circuit board, it is filled with potting compound. The bottom of the metal shell is connected to the grounding pad on the circuit board through an inner grounding guide pin.

[0007] Furthermore, the bottom of the aforementioned receiving cavity is provided with a groove, four guide pin fixing seats are provided at the four corners of the groove, a resin plate is provided at the bottom of the groove, a circuit board support step is provided around the bottom of the receiving cavity, the circuit board support step is higher than the guide pin fixing seat, the bottom surface of the circuit board contacts the circuit board support step, and the four guide pins are located on the guide pin fixing seat.

[0008] Furthermore, the metal casing base plate extends outward from both ends to form an extension, and a mounting through hole is provided in the middle of the extension. The metal casing sidewall opposite the mounting through hole is provided with an inwardly convex arc-shaped structure, and the arc-shaped structure is coaxial with the mounting through hole.

[0009] Furthermore, the top of the aforementioned metal casing is provided with an inner recessed step, the metal cover plate is embedded in the step for sealing and the top surface is flush with the top surface of the metal casing, the bottom of the metal cover plate is provided with a boss, the boss is embedded in the side wall of the metal casing, and an insulating film layer is provided at the bottom of the boss.

[0010] Furthermore, the top surface and surrounding sides of the aforementioned metal cover plate are subjected to copper-nickel plating surface treatment.

[0011] Furthermore, the circuit structure of the aforementioned filter includes differential-mode inductors L1, L2, L3, and L4. One input terminal of differential-mode inductors L1 and L2 is connected to the positive input terminal P and the negative input terminal N, respectively. The other end of differential-mode inductor L1 is connected to one input terminal of common-mode inductor L3 and one end of capacitor C1. The other end of differential-mode inductor L2 is connected to the other input terminal of common-mode inductor L3 and the other end of capacitor C1. One output terminal of common-mode inductor L3 is connected to capacitor C2. One end of capacitor C3 and capacitor C5 is connected to one input end of common mode inductor L4. The other output end of common mode inductor L3 is connected to the other end of capacitor C2, the other end of capacitor C3, one end of capacitor C6, and the other input end of common mode inductor L4. The other ends of capacitor C5 and capacitor C6 are connected to the ground terminal. One output end of common mode inductor L4 is connected to one end of capacitor C4 and the positive output segment P'. The other output end of common mode inductor L4 is connected to the other end of capacitor C4 and the positive output segment N'.

[0012] Furthermore, the aforementioned common-mode inductors L3 and L4 are symmetrically arranged on the input and output sides of the circuit board.

[0013] The beneficial effects of this utility model are as follows: Compared with the prior art, the filter of this utility model realizes the formation of a multi-stage LC filter circuit in a sufficiently small space, providing high suppression capability. At the same time, the filter is made of metal packaging, which can also resist interference itself. Attached Figure Description

[0014] Figure 1 This is a three-dimensional structural diagram of a filter used for electromagnetic interference suppression in motor control.

[0015] Figure 2 This is a schematic diagram of the front view structure of a filter used for electromagnetic interference suppression in motor control;

[0016] Figure 3 yes Figure 2 Schematic diagram of the cross-sectional structure of the middle AA section;

[0017] Figure 4 This is a top view of a filter used for electromagnetic interference suppression in motor control (with the metal cover removed).

[0018] Figure 5 yes Figure 4 Schematic diagram of the BB structure;

[0019] Figure 6 This is a schematic diagram of the three-dimensional structure of the metal casing;

[0020] Figure 7 This is a three-dimensional structural diagram of the metal casing from another perspective;

[0021] Figure 8 This is a schematic diagram of a filter circuit used for electromagnetic interference suppression in motor control.

[0022] Figure 9 This is a schematic diagram of the structure of electrical components;

[0023] Figure 10 This is a schematic diagram of an existing filter circuit structure;

[0024] Figure 11 This is a common-mode insertion loss curve;

[0025] Figure 12 This is a differential insertion loss curve;

[0026] Figure 13 This is a test pass curve for the electromagnetic compatibility of filters used for electromagnetic interference suppression in motor control.

[0027] Figure 14This is a graph showing the failure rate of existing filters in electromagnetic compatibility tests. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1: As Figure 1-9 As shown, a filter for electromagnetic interference suppression in motor control includes a metal housing 1, a resin board 2, a circuit board 3, and a metal cover plate 4. The metal housing, metal cover plate, circuit board, resin board, two common-mode inductors, two differential-mode inductors, and six capacitors C1-C6, of which four are Cx capacitors and two are Cy capacitors.

[0030] The metal casing 1 has a receiving cavity 5 with an opening at the top. The bottom of the receiving cavity 5 has a groove 6. Four guide pin fixing seats 7 are set at the four corners of the groove 6. The bottom of the groove 6 is covered with a 0.1mm resin board 2. The resin board ensures that the electrical conductive solder joints on the circuit board are completely electrically isolated from the bottom groove inside the metal casing cavity to prevent short circuits. A circuit board support step 8 is set around the bottom of the receiving cavity 5. The circuit board support step 8 is higher than the guide pin fixing seats 7. The bottom surface of the circuit board 3 contacts the circuit board support step 8. The four guide pins are located on the guide pin fixing seats 7.

[0031] A circuit board 3 is installed inside the cavity 5. The circuit board 3 contains filter components, including capacitors C1-C6, common-mode inductors L3-L4, and differential-mode inductors L1-L2. Five pins are located at the bottom of the circuit board. Four of these pins extend beyond the bottom of the metal casing 1 and are isolated from the bottom of the metal casing 1 by glass insulators 9, which provide electrical isolation. The four pins are designated as positive input terminal 10, negative input terminal 11, positive output terminal 12, and negative output terminal 13. 3 are respectively connected to the positive input terminal IN+, negative input terminal IN-, positive output terminal OUT+, and negative output terminal OUT- of the circuit board. The fifth lead is the ground terminal 14, which is fixedly connected to the bottom of the metal shell 1. The metal cover plate 4 covers the opening of the metal shell 1. After the circuit board 3 is installed in the receiving cavity 5, it is filled with potting compound. The main purpose of potting is to protect the components, increase the vibration resistance, heat dissipation, and moisture resistance of the internal components, and improve product reliability. The bottom of the metal shell 1 is connected to the grounding pad (i.e., ground terminal G) on the circuit board through the inner grounding lead 15.

[0032] To facilitate the installation of the metal casing, the bottom plate of the metal casing 1 extends outward at both ends to form an extension 16. A mounting through hole 17 is provided in the middle of the extension 16. Screws are used to pass through the mounting through hole 17 to fix the metal casing to the circuit board of the device to be installed. In order to make full use of the space, the cavity projection surface is an irregular structure. The side wall of the metal casing 1 opposite to the mounting through hole 17 is provided with an inwardly convex arc-shaped structure 18. The arc-shaped structure 18 is coaxial with the mounting through hole 17, making full use of the space at the four corners of the cavity for circuit layout, so as to achieve the purpose of making full use of the space.

[0033] Furthermore, the metal casing 1 has an inwardly recessed step 19 at its top. The metal cover plate 4 is embedded in the step 19 for sealing, and its top surface is flush with the top surface of the metal casing 1. The bottom of the metal cover plate 4 has a boss 20 embedded in the side wall of the metal casing. An insulating film layer 21 is provided at the bottom of the boss 20. The stepped structure ensures that the boss structure of the metal cover plate and the metal casing are matched, so that after assembly, the top surface of the metal cover plate and the four sides of the metal casing cavity are on the same horizontal plane. The top surface and the four sides of the metal cover plate are copper-plated with nickel to ensure that the outer surface of the metal cover plate is conductive, forming a Faraday cage with the metal casing, which can ensure that the filter has good anti-interference ability. The boss surface of the metal cover plate is anodized to form an insulating film to prevent arcing between the internal components and the metal casing.

[0034] Both the metal casing and the leads are copper-plated with nickel to ensure the metal casing is conductive. Together with the metal cover plate, they form a Faraday cage, which ensures that the filter has good anti-interference capabilities.

[0035] Furthermore, the top surface and surrounding sides of the aforementioned metal cover plate are subjected to copper-nickel plating surface treatment to form a copper-nickel plating layer.

[0036] Existing filter circuit structures, such as Figure 10 As shown, the first-stage circuit has an L-type topology and the second-stage circuit has a π-type topology, which cannot pass the electromagnetic compatibility test. This circuit structure is difficult to satisfy the suppression effect.

[0037] The schematic diagram of the filter circuit structure is as follows: Figure 8 As shown and the specific layout are as follows Figure 9As shown, the specific structure includes differential-mode inductors L1, L2, L3, and L4. One input terminal of differential-mode inductors L1 and L2 is connected to the positive input terminal P and the negative input terminal N, respectively. The other end of differential-mode inductor L1 is connected to one input terminal of common-mode inductor L3 and one end of capacitor C1. The other end of differential-mode inductor L2 is connected to the other input terminal of common-mode inductor L3 and the other end of capacitor C1. One output terminal of common-mode inductor L3 is connected to one end of capacitors C2, C3, and C5 and one input terminal of common-mode inductor L4. The other end of the output is connected to the other end of capacitor C2, the other end of capacitor C3, one end of capacitor C6, and the other end of the input of common mode inductor L4. The other end of capacitor C5 and the other end of capacitor C6 are connected to the ground terminal. One end of the output of common mode inductor L4 is connected to one end of capacitor C4 and the positive output segment P'. The other end of the output of common mode inductor L4 is connected to the other end of capacitor C4 and the positive output segment N'. Common mode inductors L3 and L4 are symmetrically arranged on the input side and the output side of the circuit board. Differential mode inductors L1 and L2 are symmetrically arranged on the front and back sides of the circuit board.

[0038] The filter employs a three-stage LC circuit design, with the circuit board layout implementing the connection logic between the common-mode inductors (L3, L4), differential-mode inductors (L1, L2), and capacitors (C1, C2, C3, C4, C5, C6). A series connection between the common-mode inductors L3 and L4 and capacitors C5 and C6 forms a ground loop, utilizing the high impedance of the common-mode inductors and the high-pass characteristics of the capacitors to achieve common-mode suppression. The LC topology formed by L1 (L2) and C1 provides the first stage of filtering for differential-mode interference. The leakage inductance of the common-mode inductor L3, along with C1 and C2, forms a π-type topology for further filtering of differential-mode interference. Finally, the leakage inductance of the common-mode inductor L4, along with C3 and C4, forms a π-type topology for a third stage of filtering. The entire circuit effectively suppresses both common-mode and differential-mode interference on both the positive and negative lines.

[0039] Example 2: A method for manufacturing a filter for electromagnetic interference suppression in motor control, the method comprising the following steps:

[0040] 1) The metal shell and metal cover are made of 4J29 alloy material and are processed to form cavity-shaped structural parts and plate-shaped structural parts respectively. Then, the metal shell and glass are co-fired at 1400℃ to obtain a sealed and fixed connection between the glass insulator and the metal shell, thus realizing the sealed connection between the metal shell and the glass insulator.

[0041] 2) The metal casing is first sandblasted on the bottom surface, then pre-treated by degreasing and rust removal. The surface of the metal casing is cleaned, and then 2μm thick copper is plated on the inner and outer surfaces by electroplating, followed by 10~15μm thick nickel. The purpose of the double metal layer is to improve the conductivity, oxidation resistance and adhesion of the metal casing.

[0042] 3) The metal cover plate is first sandblasted on the bottom surface, then pre-treated by degreasing and derusting, and the surface of the metal cover plate is cleaned. The inner and outer surfaces are first plated with 2μm thick copper, and then plated with 10~15μm thick nickel. Finally, the raised surface of the metal cover plate is polished to remove the plating layer, and then anodized on the raised surface to form an insulating film layer with a thickness of 0.3~0.8μm.

[0043] 4) Select 1210-size ceramic capacitors C1-C6, where C1-C4 are used as Cx capacitors and C5-C6 are used as Cy capacitors;

[0044] 5) Clean the steel mesh and carrier with alcohol. Before use, ensure that the steel mesh and carrier are clean and that the openings are free of impurities.

[0045] 6) Sn-5Sb solder paste is used to solder the PAD (pad) and capacitor of the circuit board. Before use, take the solder paste out of the freezer and let it thaw at room temperature for 30-60 minutes. Then use the stirring rod to stir the solder paste repeatedly in a clockwise-counterclockwise direction for 30-60 seconds until the solder paste is in a stringy state.

[0046] 7) Fix the circuit board on the carrier and adjust the PAD of the circuit board to be consistent with the opening of the steel mesh. Close the steel mesh to ensure that the steel mesh and the circuit board on the carrier are flat.

[0047] 8) Pour the set amount of solder paste onto the stencil and use a scraper to evenly spread the solder paste into the openings so that the solder paste covers the PADs of C1-C6 on the circuit board;

[0048] 9) A 12-zone reflow oven was used for soldering the circuit board and capacitors C1-C6;

[0049] The upper and lower temperature settings for the 12 temperature zones are: 146℃, 155℃, 160℃, 170℃, 185℃, 200℃, 220℃, 240℃, 270℃, 270℃, 240℃, and 200℃. The allowable temperature adjustment tolerance for each zone is ±5℃, depending on the quantity of reflow soldering. The reflow soldering chain speed is set to 0.70 m / min.

[0050] 10) After the capacitors C1-C6 are reflow soldered, allow them to cool naturally before soldering the common mode inductors L3-L4 and differential mode inductors L1-L2.

[0051] 11) To achieve a significant suppression effect in the 20kHz~75kHz range, the inductance of the common-mode inductor should be no less than 10mH, and the inductance of the differential-mode inductor should be no less than 100uH. The common-mode inductor is manufactured using a magnetic ring made of 1K107F nanocrystalline amorphous tape material with a permeability greater than 80000. The differential-mode inductor is manufactured using a magnetic ring made of microcrystalline iron-based amorphous tape material with a permeability not exceeding 1200. To reduce product height, high-temperature enameled round copper wire is threaded onto the magnetic ring of the common-mode or differential-mode inductor to form a coil. The free end of the high-temperature enameled round copper wire after removing the enamel is used as the lead-out terminal of the common-mode or differential-mode inductor. Sn-5Sb solder wire is used to solder the lead-out terminals of the common-mode or differential-mode inductor into the through-holes of the circuit board, and excess wire is trimmed. The soldering temperature setting is 400℃±30℃.

[0052] 12) After the circuit board is soldered in steps 10) and 11), use JD-086 board cleaning solution to soak and clean the circuit board. Soak the circuit board in the board cleaning solution for 5 to 10 minutes, and then use a dense and soft bristle toothbrush to brush the solder joints, the circuit board and the components on the circuit board back and forth. The brushing cycle should be no less than 10 times. After the first cleaning is completed, replace the board cleaning solution and soak and clean it again.

[0053] 13) After the cleaned circuit board has air-dried naturally, continue soldering the leads and grounding terminals on the circuit board. The leads include the positive input terminal, the negative input terminal, the positive output terminal, and the negative output terminal.

[0054] 14) Place the resin board into the groove in the receiving cavity of the metal casing, then align the lead-out holes of the circuit board with the lead-out terminals inside the metal casing cavity, and pass the lead-out terminals through the through holes to install the circuit board. (Step 6 is to solder the capacitor pads to the corresponding pad positions on the circuit board, step 11 is to solder the common-mode inductor and differential-mode inductor solder joints, and step 14 is to solder the lead-out terminals inside the metal casing cavity.) Figure 6 (10, 11, 12, 13) and grounding terminal ( Figure 6 15 in the middle).

[0055] 15) First, set the heating plate (the purpose of heating is preheating to reduce the temperature difference between the solder leads and the ground terminal, improving soldering quality) to 100℃ and wait for the heating plate to reach the required temperature. Then, place the metal casing with the circuit board installed, along with the fixing carrier (the fixing carrier is a fixture for fixing the metal casing to be soldered, preventing the casing from being unsecured during soldering and preventing the metal casing from moving during soldering, which is not conducive to soldering), on the heating plate and heat for 1-2 minutes. Then, use a soldering iron and Sn-5Sb solder wire to solder the through holes of the circuit board leads, ensuring that the input, output, and ground terminals are soldered well. The soldering iron temperature setting is 400℃±30℃.

[0056] 16) Soak and clean the welded product from step 15) again with the board cleaning water for 5 minutes, then let it stand at room temperature for 30 minutes, and then bake it in an oven to ensure that the product is dry; the baking temperature and time settings are 130℃±10℃ and 60 minutes±5 minutes.

[0057] 17) Use two-component silicone sealant to pot the cavity of the metal casing, and control the potting height to just cover the surfaces of the highest common-mode inductors L3-L4 and differential-mode inductors L1-L2.

[0058] 18) Cover with a metal cover plate and use laser sealing welding to remelt the gap between the metal cover plate and the metal shell together to form a sealing weld pattern;

[0059] 19) Finally, the product markings are etched onto the center of the metal cover using a laser marking process. The markings may include, but are not limited to, the model number, name, manufacturer, lead-out symbol, batch number, etc.

[0060] 20) By testing the filter's insertion loss, the differential-mode insertion loss suppression capability can reach up to 100dB in the 10kHz~30MHz range, and the common-mode insertion loss suppression capability can reach up to 90dB in the 10kHz~30MHz range. Figure 11-12 As shown.

[0061] The filter of this invention is showing significant results in electromagnetic capacitance tests, such as... Figure 14 As shown, during the R102 conducted signal test, the existing filter exhibited significant interference exceeding the limit in the 10kHz~10MHz range, with the exceedance approaching 50dB, resulting in a failed test. After rectification with this utility model, as shown... Figure 13 As shown, the signal does not exceed the limit at all in the 10kHz~10MHz range, with a margin of at least 10dB, and the test passed.

[0062] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the protection scope of the claims.

Claims

1. A filter for electromagnetic interference suppression in motor control, characterized in that, The device includes a metal casing, a circuit board, and a metal cover. The metal casing has a cavity with an opening at the top, inside which the circuit board is installed. The circuit board contains filter components. Five pins are located at the bottom of the circuit board. Four of the pins extend out of the bottom of the metal casing and are isolated from the bottom of the metal casing by glass insulators. The four pins are the positive input terminal, the negative input terminal, the positive output terminal, and the negative output terminal, respectively. The fifth pin is the grounding terminal and is fixedly connected to the bottom of the metal casing. The metal cover covers the opening of the metal casing. After the circuit board is installed in the cavity, it is filled with potting compound. The bottom of the metal casing is connected to the grounding pad on the circuit board through an internal grounding pin.

2. The filter for electromagnetic interference suppression in motor control according to claim 1, characterized in that, The bottom of the receiving cavity is provided with a groove, and four guide pin fixing seats are provided at the four corners of the groove. The bottom of the groove is provided with a resin plate. Circuit board support steps are provided around the bottom of the receiving cavity. The circuit board support steps are higher than the guide pin fixing seats. The bottom surface of the circuit board contacts the circuit board support steps. The four guide pins are located on the guide pin fixing seats.

3. A filter for electromagnetic interference suppression in motor control according to claim 1, characterized in that, The metal casing base plate extends outward from both ends to form an extension section. A mounting through hole is provided in the middle of the extension section. The metal casing sidewall opposite the mounting through hole is provided with an inwardly convex arc-shaped structure, which is coaxial with the mounting through hole.

4. A filter for electromagnetic interference suppression in motor control according to claim 1, characterized in that, The top of the metal casing is provided with an inner recessed step, and the metal cover plate is embedded in the step for sealing, with its top surface flush with the top surface of the metal casing. The bottom of the metal cover plate is provided with a boss, which is embedded in the side wall of the metal casing, and an insulating film layer is provided at the bottom of the boss.

5. A filter for electromagnetic interference suppression in motor control according to claim 4, characterized in that, The top and four sides of the metal cover plate are treated with copper-nickel plating.

6. A filter for electromagnetic interference suppression in motor control according to claim 2, characterized in that, The filter circuit structure includes differential-mode inductors L1, L2, L3, and L4. The input terminals of differential-mode inductors L1 and L2 are connected to the positive input terminal P and the negative input terminal N, respectively. The other end of differential-mode inductor L1 is connected to one input terminal of common-mode inductor L3 and one end of capacitor C1. The other end of differential-mode inductor L2 is connected to the other input terminal of common-mode inductor L3 and the other end of capacitor C1. One output terminal of common-mode inductor L3 is connected to one end of capacitors C2, C3, and C5 and one input terminal of common-mode inductor L4. The other output terminal of common-mode inductor L3 is connected to the other ends of capacitors C2, C3, and C6 and the other input terminal of common-mode inductor L4. The other ends of capacitors C5 and C6 are connected to ground. One output terminal of common-mode inductor L4 is connected to one end of capacitor C4 and the positive output segment P'. The other output terminal of common-mode inductor L4 is connected to the other end of capacitor C4 and the positive output segment N'.

7. A filter for electromagnetic interference suppression in motor control according to claim 6, characterized in that, Common mode inductors L3 and L4 are symmetrically arranged on the input and output sides of the circuit board.

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