Design method of marine low-to-ground capacitance filter

Abstract

The invention belongs to the technical field of electromagnetic compatibility control design, and particularly relates to a design method of a marine low-to-ground capacitance filter. The method comprises the specific steps that firstly, an inductor is adopted as a main filtering device, a magnetic core of the inductor is made of an iron-based nanocrystalline material for a low-frequency band below 100 kHz, a magnetic core of the inductor is made of a MnZn magnetic material for a low-frequency band from 100 kH to 1 MHz, and a magnetic core of the inductor is made of a NiZn magnetic material for a high-frequency band above 1 MHz; thirdly, based on the designed inductor, designing a low-frequency and high-frequency combined multi-stage filter circuit; the filter circuit comprises a plurality of common-mode inductors which are sequentially connected in series, differential-mode capacitors Cx which are connected to the two ends of the common-mode inductors in parallel, a common-mode capacitor Cy which is connected between a live wire and the ground in parallel, and a common-mode capacitor Cy which is connected between a zero wire and the ground in parallel; and finally, modular packaging and glue filling are carried out, so that the inductor of the filter circuit is parallel to the shell, the center position of the filter circuit is located at the center position of the shell, and overall insulation glue filling is not carried out.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic compatibility control design, and in particular relates to a design method for a marine low-ground capacitance filter. Background Art

[0002] The power capacity of modern marine power systems is constantly increasing, the use of power electronic equipment is increasing day by day, the electromagnetic wave spectrum used is constantly expanding, the working frequency is becoming increasingly dense, and the electromagnetic environment in the ship cabin is more complex. The rectifier components, switch tubes and other components of the power supply are the main sources of electromagnetic interference generated by the equipment itself. Electromagnetic interference will be transmitted to other devices through the power line, causing interference to sensitive electronic equipment in the same electromagnetic environment, which may cause abnormal operation.

[0003] On the other hand, compared with land-based power systems and electronic equipment, the "grounding" in common working scenarios of ships is connected to the hull, and there is no real "ground". The electromagnetic interference generated by various interference source equipment in the ship's cabin will flow into the hull "ground" through the grounding wire and will not disappear directly. These interferences will enter the electronic components through the grounding wire and ground capacitance of the electronic equipment and cause interference.

[0004] Filters are key components for electromagnetic interference protection. However, due to their working principles, all filters have capacitance to ground. While filtering out electromagnetic interference, the capacitance to ground will reversely introduce electromagnetic interference from the ship hull ground into sensitive equipment, causing electromagnetic interference risks. To solve the above problems, it is necessary to significantly reduce the capacitance of the filter to ground without affecting the performance of the filter, so as to effectively enhance the electromagnetic interference suppression performance of the filter. Summary of the invention

[0005] In view of this, the present invention provides a method for designing a ship-based low-ground capacitance filter, which can achieve the function of broadband conducted electromagnetic interference filtering, while significantly reducing the ground capacitance and reducing the electromagnetic interference of the ship hull ground current.

[0006] The technical solution for implementing the present invention is as follows:

[0007] A design method for a marine low ground capacitance filter, the specific process is:

[0008] First, inductors are used as the main filtering components. For low frequency bands below 100kHz, the core of the inductor is made of iron-based nanocrystalline material. For low frequency bands from 100kH to 1MHz, the core of the inductor is made of MnZn magnetic material. For high frequency bands above 1MHz, the core of the inductor is made of NiZn magnetic material.

[0009] Thirdly, based on the designed inductor, a multi-stage filter circuit combining low frequency and high frequency is designed; the filter circuit comprises: a plurality of common mode inductors connected in series in sequence, a differential mode capacitor Cx connected in parallel to both ends of the common mode inductor, a common mode capacitor Cy connected in parallel between the live wire and the ground, and a common mode capacitor Cy connected in parallel between the neutral wire and the ground;

[0010] Finally, modular packaging and glue potting are performed so that the inductance of the filter circuit is parallel to the shell, the center position of the filter circuit is located at the center position of the shell, and the overall insulation glue potting is not performed.

[0011] Furthermore, the NiZn common mode inductor of the present invention adopts a toroidal magnetic core.

[0012] Furthermore, the filter housing of the present invention is made of stainless steel, and the shielding body is made of conductive oxidized aluminum on the surface.

[0013] Furthermore, the filtering circuit of the present invention includes two-stage low-frequency common-mode inductors Lc1 and Lc2 and one-stage high-frequency common-mode inductor Lc3, and the three inductors are cascaded; the common-mode inductor Lc1 is made of iron-based nanocrystalline material, the common-mode inductor Lc2 is made of low magnetic permeability MnZn ferrite material, and the common-mode inductor Lc3 is made of NiZn ferrite material.

[0014] Furthermore, the number of differential mode capacitors Cx connected in parallel to both ends of the common mode inductor is three, and a protective resistor is connected in parallel to both ends of each differential mode capacitor Cx.

[0015] Furthermore, the inductance of the common-mode inductor Lc1 of the present invention is 30mH; the inductance of the common-mode inductor Lc2 is 3mH; the inductance of the common-mode inductor Lc3 is 50uH; the capacitance value of the common-mode capacitor Cy is 0.23nF; and the capacitance value of the differential-mode capacitor Cx is 10uF.

[0016] Beneficial effects:

[0017] Aiming at the problem of conducted electromagnetic interference of ship power system and electromagnetic interference of hull ground current, the present invention proposes a design method of a large-bandwidth and low-ground capacitance power supply filter, which can realize the function of filtering broadband conducted electromagnetic interference, and at the same time greatly reduce the ground capacitance and reduce the electromagnetic interference of hull ground current. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. 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 creative work.

[0019] Figure 1 It is a design flow chart of the present invention;

[0020] Figure 2 It is a low-frequency filtering circuit diagram of a marine low-to-ground capacitance filter of the present invention;

[0021] Figure 3 is a common mode circuit parameter of a low-frequency filter circuit of a marine low-ground capacitance filter of the present invention;

[0022] Figure 4 It is the common mode insertion loss of the low-frequency filter circuit of the marine low-ground capacitance filter of the present invention;

[0023] Figure 5 is a differential mode circuit parameter of a low-frequency filter circuit of a marine low-ground capacitance filter of the present invention;

[0024] Figure 6 is the differential mode insertion loss of the low-frequency filter circuit of the marine low-ground capacitance filter of the present invention;

[0025] Figure 7 It is the distributed capacitance of the high frequency filter circuit of the marine low-to-ground capacitance filter of the present invention to the metal shell;

[0026] Figure 8 It is a three-dimensional structural diagram of the position where the toroid of the inductor element is parallel to the ground;

[0027] Fig. 9 It is a three-dimensional structural diagram of the position of the inductor element ring perpendicular to the ground;

[0028] Fig.10 It is a circuit principle diagram of a filter circuit of a marine low-ground capacitance filter of the present invention;

[0029] Fig.11 It is the common mode circuit simulation schematic diagram of the filter circuit;

[0030] Fig.12 It is the insertion loss simulation result of the common-mode circuit simulation of the filter circuit;

[0031] Fig.13 It is the simulation schematic diagram of the differential mode circuit of the filter circuit;

[0032] Fig.14 It is the insertion loss simulation result of the differential mode circuit simulation of the filter circuit. DETAILED DESCRIPTION

[0033] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0034] It should be noted that the following embodiments and features in the embodiments may be combined with each other in the absence of conflict; and, based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making any creative work are within the scope of protection of the present disclosure.

[0035] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein may be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present disclosure, it should be understood by those skilled in the art that an aspect described herein may be implemented independently of any other aspect, and two or more of these aspects may be combined in various ways. For example, any number of aspects described herein may be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein may be used to implement this device and / or practice this method.

[0036] The present application embodiment provides a method for designing a low-ground capacitance filter for a ship, and the specific process is as follows:

[0037] Step 1: Use inductor as the main filtering component. For the low frequency band below 100kHz, the magnetic core of the inductor is made of iron-based nanocrystalline material. For the low frequency band from 100kH to 1MHz, the magnetic core of the inductor is made of MnZn magnetic material. For the high frequency band above 1MHz, the magnetic core of the inductor is made of NiZn magnetic material.

[0038] Step 2: Based on the designed inductor, a multi-stage filter circuit combining low frequency and high frequency is designed; the filter circuit includes: a plurality of common mode inductors connected in series in sequence, a differential mode capacitor Cx connected in parallel to both ends of the common mode inductor, a common mode capacitor Cy connected in parallel between the live wire and the ground, and a common mode capacitor Cy connected in parallel between the neutral wire and the ground;

[0039] Step three: modular packaging and glue pouring, so that the center position of the filter is at the center position of the shell, and the overall insulation glue pouring is not performed.

[0040] The principles and considerations of the design process of the embodiment of the present application are described in detail below. Figure 1 As shown in the figure, the design process of marine low ground capacitance filter is shown in the figure.

[0041] Furthermore, in this embodiment, only the inductor is used as the main filter component to achieve the beneficial effects of wide insertion loss bandwidth and small filter capacitance to ground.

[0042] On the one hand, in order to meet the needs of broadband filtering, the above design must be implemented using a multi-stage filtering circuit that combines low frequency and high frequency; on the other hand, in order to reduce the filter's capacitance to ground, the entire filtering circuit should not use common-mode capacitors, that is, functional capacitance to ground, but only use inductors as the main filtering components to achieve the beneficial effects of wide insertion loss bandwidth and small filter capacitance to ground.

[0043] Furthermore, for low frequency bands below 100kHz, the magnetic core of the inductor is made of iron-based nanocrystalline material, and for low frequency bands from 100kH to 1MHz, the magnetic core of the inductor is made of MnZn magnetic material to achieve common mode filtering function. The specific inductance value needs to be determined in combination with the insertion loss requirements of this frequency band.

[0044] In order to make the normal transmission signal in the passband as unaffected as possible, the attenuation in the stopband should be large. The stopband of the Butterworth filter function presents the flattest characteristics, so the marine low-to-ground capacitance filter selects the Butterworth filter function model to design the passive low-pass filter circuit. The insertion loss calculation formula of the Butterworth low-pass filter function is:

[0045]

[0046] In the formula, ω is the normalized frequency, ω c =3dB is the cut-off frequency, n is the order of the filter (the number of L and C components). Since the capacitance to ground needs to be controlled, the use of capacitor components should be reduced, and its filtering performance is mainly achieved by large inductance. For this reason, the inductor core needs to use amorphous, MnZn magnetic materials with good low-frequency performance.

[0047] Since the filter is limited by temperature rise and voltage drop, conventional differential mode inductors cannot be used to suppress low-frequency interference. It is necessary to select inductors that are not easily saturated and have higher performance in the frequency band below 100kHz. At the same time, simulation is combined with design verification to ensure that the insertion loss requirements of the low-frequency band are met.

[0048] Furthermore, for high frequency bands above 1MHz, an inductor with a NiZn magnetic material with good high frequency performance as the magnetic core is used to achieve the common mode filtering function. The specific inductance value needs to be determined in combination with the insertion loss requirements of the frequency band.

[0049] Due to the need to control the capacitance to ground, the use of capacitor components should be reduced, and inductor components with better suppression effect in the high-frequency band should be selected. NiZn magnetic materials with good high-frequency performance should be used to make common-mode inductor components.

[0050] Furthermore, the functional inductor device is modularly packaged and glue-filled, and is arranged parallel to the filter structure ground with the center of the device at the center of the shell, so as to meet the insulation and structural strength of the filter and achieve the beneficial effect of small filter-to-ground capacitance.

[0051] Since the capacitance to ground needs to be controlled, functional capacitance to ground cannot be used in circuit design. However, there is distributed capacitance between the filter circuit and the filter housing. At the same time, the filter has a large current (high carrying power) and high broadband insertion loss requirements, which leads to a large volume of the filter circuit, and the distributed capacitance of the filter circuit to the ground (filter housing) is also large. According to the definition of capacitance, two conductor plates close to each other, with dielectric material ε filled in between, constitute a capacitor. The calculation formula for flat plate capacitance is shown in Formula 2:

[0052]

[0053] Where: ε—dielectric constant (F / m); S—conductor plate area; d—the distance between two conductor plates.

[0054] From the formula we can see that:

[0055] (1) The larger the dielectric constant ε of the dielectric, the more obvious the degree of polarization and the larger the capacitance;

[0056] (2) The larger the area of ​​the conductor plate, the greater the capacitance;

[0057] (3) The smaller the distance between the conductor plates, the greater the electric field strength at the same voltage, the more obvious the polarization of the dielectric, and the greater the capacitance.

[0058] Therefore, the main factors affecting the filter's capacitance to ground are:

[0059] (1) The distributed capacitance is related to the position of the filter element relative to the housing, that is, the placement and form of the inductor in the housing;

[0060] (2) It is related to whether insulating glue is used to pot the filter circuit.

[0061] Finally, by controlling the functional capacitance to ground and controlling the distributed capacitance to ground by not performing overall insulation glue potting, the capacitance to ground of the filter was ensured to meet the requirements.

[0062] Furthermore, the low-frequency and high-frequency band filter circuits are cascaded to design a final filter circuit.

[0063] Furthermore, the filter housing is made of 316L stainless steel, and the shield is made of 2A12 hard aluminum with conductive oxidation treatment on the surface to meet the anti-corrosion requirements of the harsh environment of high temperature and high humidity for marine filters. Continuous welding is also used to meet the vibration resistance requirements of the filter structure.

[0064] The following is a detailed explanation of the marine filter with an operating frequency of 10kHz to 10MHz and a capacitance to ground of no more than 2nF.

[0065] Step 1: In the design of the low-frequency 10kHz~100kHz filter circuit, since the filter is in the 10k~100kHz frequency band, it mainly involves differential mode insertion loss, so the Butterworth filter function should be based on the differential mode circuit. In order to achieve the technical indicators of the low frequency band, the fifth-order Butterworth filter function is used. The filter circuit has two common-mode inductors and one differential-mode inductor. Figure 2 As shown, Cy is a common mode capacitor with a capacitance to ground of pF level in the circuit, Lc1 and Lc2 are common mode inductors, Ld is a differential mode inductor, and Cx1 is a differential mode capacitor.

[0066] According to the topological structure of common mode and differential mode circuits, the common mode and differential mode insertion loss of low frequency filter circuits are simulated. Figure 3 As shown, the insertion loss is Figure 4 As shown; differential mode circuit parameters are as follows Figure 5 The insertion loss results are shown in Figure 6 shown.

[0067] Step 2. Considering the voltage drop of the filter, the topological configuration of the high-frequency filter circuit is similar to that of the low-frequency circuit. It is also composed of high-frequency common-mode inductors and common-mode and differential-mode capacitors. The difference is that the common-mode insertion loss of high frequency is more closely related to the common-mode capacitance. Due to the need to control the capacitance to ground, the use of capacitor components should be reduced, and inductors with better suppression effects in the high-frequency band should be selected. NiZn ferrite has low magnetic permeability and high resistance, which is suitable for high-frequency occasions. NiZn ferrite can be used in the frequency range of 1MHz to 300MHz. The main features are low magnetic permeability, high resistivity, and low high-frequency eddy current loss. It is the inductor core material with the best magnetic properties in the high-frequency band above MHz. Therefore, NiZn magnetic materials with good high-frequency performance are used to make common-mode inductor components. In order to avoid magnetic saturation, high-frequency inductors still use common-mode inductors. Considering the actual power requirements, NiZn common-mode inductors use toroidal magnetic cores. Since the common-mode inductor of large current is large in size, it will increase the distributed capacitance from the filter circuit to the ground. For this reason, differential-mode capacitors with appropriate parameters are used, which are connected in parallel to achieve large differential-mode capacitance, thereby reducing the volume of the common-mode inductor.

[0068] Step 3: When designing the filter circuit, the limitation of the filter's functional capacitance to ground has been taken into consideration. Furthermore, the control of the filter circuit's capacitance to ground focuses on the control of the filter circuit's distributed capacitance to ground. The capacitance to ground is further controlled by the arrangement of the filter's internal components and the packaging design.

[0069] In this example, the filter housing is made of metal material to ensure the structural and installation strength. For the filter in this example, the elements that constitute the ground capacitance are the filter circuit (one electrode) and the filter housing (the other electrode). In the filter circuit, only the inductor is a conductor. Therefore, the determining factor of the filter circuit electrode is the inductor.

[0070] In this example, according to formula (2), Figure 7 As shown, the filter circuit and the six surfaces of the metal shell form distributed capacitance (set as Cy1, Cy2, Cy3, Cy4, Cy5, Cy6), and the L and N lines of the filter circuit and the metal shell form distributed capacitance (set as Cy7, Cy8). Since all the above capacitors are in parallel, according to the parallel formula of capacitors, the total distributed capacitance of the filter circuit and the metal shell is the sum of the values ​​of the above eight capacitors.

[0071] by Figure 8 , Fig. 9 Taking the two filter circuits shown in the figure as an example, Cy2 relative to the bottom surface of the filter housing is different due to the different areas of the inductor element projected on the bottom surface. Obviously, the inductor element ring in the filter circuit is placed perpendicular to the ground, and the S formed with the ground is smaller, and the distributed capacitance formed is also smaller.

[0072] Since the distributed capacitance is proportional to the area Si (different shell surfaces) of the circuit and inversely proportional to the distance di (different shell surfaces), the larger the volume of the filter circuit, the closer the distance to the shell, and the larger the area parallel to the shell, the larger the distributed capacitance. For this reason, the volume of the filter circuit (using new magnetic conductive materials) and the area parallel to the shell (the installation position of the filter inductor relative to the shell) must be minimized. For this reason, the volume of the filter circuit must be minimized and a new structure that reduces distributed capacitance must be used.

[0073] On the other hand, in order to optimize the ε parameter in formula (2), traditional filters usually use potting materials to fill the gap between the filter circuit and the metal shell to fix the filter circuit and increase the insulation strength. However, it can be seen from formula (2) that since the ε of the potting material must be greater than that of air, potting will inevitably increase the distributed capacitance. For this reason, the potting material cannot be used to pot the filter circuit, and other fixing methods must be used to fix the filter circuit.

[0074] After simulation optimization design, the low-frequency and high-frequency filter circuits are finally cascaded to form the following complete filter circuit design scheme: It consists of "two-stage common mode (low frequency)" + one-stage common mode (high frequency). The circuit schematic diagram is as follows: Fig.10 As shown in the figure, the common mode and differential mode circuit simulation parameters and insertion loss of the filter circuit are as follows Figure 11-14 As shown, where:

[0075] Common mode inductor Lc1: Made of iron-based nanocrystalline material, it achieves high insertion loss at low frequencies of 10k to 100kHz and small size, laying the necessary foundation for the realization of extremely low distributed capacitance of the filter;

[0076] Common mode inductor Lc2: Made of low permeability MnZn ferrite material, the inductance is relatively stable in a wide frequency range, which can improve the insertion loss in the intermediate frequency band of 100kHz to 10MHz;

[0077] Common mode inductor Lc3: Made of NiZn ferrite material, it achieves high frequency insertion loss of 10M~100MHz.

[0078] The circuit design of the entire filter is based on electromagnetic simulation. After the performance of the sample, it can meet the insertion loss design index and leave enough margin. The specific parameters of the filter are: common mode inductor Lc1 inductance: 30mH; common mode inductor Lc2 inductance: 3mH; common mode inductor Lc3 inductance: 50uH; common mode capacitor Cy capacitance value: 0.23nF; differential mode capacitor Cx capacitance value: 10uF. It can be seen from the above circuit parameters that the capacitance value of each line to ground capacitor in the AC filter circuit is only 0.23nF.

[0079] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for designing a low ground capacitance filter for a ship, characterized in that: The specific process is: First, inductors are used as the main filtering components. For low frequency bands below 100kHz, the core of the inductor is made of iron-based nanocrystalline material. For low frequency bands from 100kH to 1MHz, the core of the inductor is made of MnZn magnetic material. For high frequency bands above 1MHz, the core of the inductor is made of NiZn magnetic material. Thirdly, based on the designed inductor, a multi-stage filter circuit combining low frequency and high frequency is designed; The filter circuit comprises: a plurality of common mode inductors connected in series in sequence, a differential mode capacitor Cx connected in parallel to both ends of the common mode inductors, a common mode capacitor Cy connected in parallel between the live wire and the ground, and a common mode capacitor Cy connected in parallel between the neutral wire and the ground; Finally, modular packaging and glue potting are performed so that the inductance of the filter circuit is parallel to the shell, the center position of the filter circuit is located at the center position of the shell, and the overall insulation glue potting is not performed.

2. The method for designing a low ground capacitance filter for a ship according to claim 1, characterized in that: The NiZn common mode inductor adopts a circular ring magnetic core.

3. The method for designing a low ground capacitance filter for a ship according to claim 1, characterized in that: The filter shell is made of stainless steel, and the surface is made of conductive oxidized aluminum to make a shielding body.

4. The method for designing a low ground capacitance filter for a ship according to claim 1, characterized in that: The filtering circuit includes two-stage low-frequency common-mode inductors Lc1 and Lc2 and one-stage high-frequency common-mode inductor Lc3, and the three inductors are cascaded; the common-mode inductor Lc1 is made of iron-based nanocrystalline material, the common-mode inductor Lc2 is made of low-permeability MnZn ferrite material, and the common-mode inductor Lc3 is made of NiZn ferrite material.

5. The method for designing a low ground capacitance filter for a ship according to claim 4, characterized in that: There are three differential mode capacitors Cx connected in parallel to the two ends of the common mode inductor, and a protective resistor is connected in parallel to the two ends of each differential mode capacitor Cx.

6. The method for designing a low ground capacitance filter for a ship according to claim 5, characterized in that: The inductance of the common mode inductor Lc1 is 30mH; the inductance of the common mode inductor Lc2 is 3mH; the inductance of the common mode inductor Lc3 is 50uH; the capacitance value of the common mode capacitor Cy is 0.23nF; the capacitance value of the differential mode capacitor Cx is 10uF.

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