A method for designing a low-to-ground capacitance filter for a ship

Abstract

The application belongs to the technical field of electromagnetic compatibility control design, and particularly relates to a marine low-ground-capacitance filter design method. The method specifically comprises the following steps: firstly, using an inductor as a main filter device, for a low-frequency band below 100 kHz, a magnetic core of the inductor uses an iron-based nanocrystalline material, for a low-frequency band from 100 kHz to 1 MHz, the magnetic core of the inductor uses MnZn magnetic material, and for a high-frequency band above 1 MHz, the magnetic core of the inductor uses NiZn magnetic material; secondly, 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, 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 a live wire and the ground, and a common-mode capacitor Cy connected in parallel between a zero wire and the ground; finally, modular packaging and glue filling are performed, 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 performed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic compatibility control design, and particularly relates to a marine low-ground-capacitance filter design method. BACKGROUND

[0002] The power capacity of modern marine power systems is continuously improved, the use of power electronic equipment is increasing day by day, the electromagnetic wave spectrum used is continuously expanding, the working frequency is increasingly dense, and the electromagnetic environment in the cabin of the ship is more complex. The rectifier devices, switching tubes and other devices of the power supply are the main interference sources of electromagnetic interference generated by the devices themselves, and the electromagnetic interference will be conducted to other devices through the power supply line, causing the sensitive electronic devices in the same electromagnetic environment to be disturbed, which may cause abnormal work.

[0003] On the other hand, compared with the land power system and electronic equipment, the "ground" in the common working scene of the ship is connected to the hull, and there is no real "ground", and the electromagnetic interference generated by each interference source device in the cabin of the ship will flow into the hull "ground" through the grounding line and will not directly disappear, and the interference will enter the electronic components through the grounding line and the ground capacitance of the electronic equipment and then cause interference.

[0004] The filter is a key device for electromagnetic interference protection, but due to the working principle, all filters have a ground capacitance, which will introduce electromagnetic interference from the ship hull ground into the sensitive device in the opposite direction while filtering electromagnetic interference, causing electromagnetic interference risk. In order to solve the above problems, it is necessary to greatly reduce the ground capacitance of the filter without affecting the performance of the filter, and effectively strengthen the electromagnetic interference suppression performance of the filter. SUMMARY

[0005] Therefore, the application provides a marine low-ground-capacitance filter design method, which can realize the function of filtering wideband conducted electromagnetic interference, while greatly reducing the ground capacitance and reducing the ship hull ground current electromagnetic interference.

[0006] The technical scheme of the application is as follows:

[0007] A marine low-ground-capacitance filter design method, the specific process is as follows:

[0008] First, an inductor is used as the main filter device, the magnetic core of the inductor uses iron-based nanocrystalline material for low-frequency bands below 100 kHz, MnZn magnetic material for low-frequency bands from 100 kHz to 1 MHz, and NiZn magnetic material for high-frequency bands above 1 MHz;

[0009] Furthermore, based on the designed inductor, a multi-stage filter circuit combining low-frequency and high-frequency components is designed; the filter circuit includes: multiple common-mode inductors connected in series, a differential-mode capacitor Cx connected in parallel across the common-mode inductors, a common-mode capacitor Cy connected in parallel between the live wire and ground, and a common-mode capacitor Cy connected in parallel between the neutral wire and ground.

[0010] Finally, modular encapsulation and potting are performed so that the inductance of the filter circuit is parallel to the casing, the center of the filter circuit is located at the center of the casing, and no overall insulating potting is performed.

[0011] Furthermore, the NiZn common-mode inductor described in this invention employs a toroidal magnetic core.

[0012] Furthermore, the filter housing of the present invention is made of stainless steel, and the surface is made of conductive anodized aluminum to form a shield.

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

[0014] Furthermore, the differential mode capacitor Cx connected in parallel across the common mode inductor in this invention comprises three capacitors, and a protection resistor is connected in parallel across each differential mode capacitor Cx.

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

[0016] Beneficial effects:

[0017] This invention proposes a design method for a high-bandwidth, low-to-ground capacitance power supply filter to address the problems of conducted electromagnetic interference in ship power systems and electromagnetic interference from hull ground current. This method can achieve the function of filtering out broadband conducted electromagnetic interference while significantly reducing the capacitance to ground and minimizing electromagnetic interference from hull ground current. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a design flowchart of the present invention;

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

[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 application;

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

[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 application;

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

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

[0026] Figure 8 is a three-dimensional structure schematic diagram of a position of an inductance element ring parallel to the ground;

[0027] Figure 9 is a three-dimensional structure schematic diagram of a position of an inductance element ring perpendicular to the ground;

[0028] Figure 10 is a circuit principle diagram of a filter circuit of a marine low-ground capacitance filter of the present application;

[0029] Figure 11 is a common-mode circuit simulation principle diagram of a filter circuit;

[0030] Figure 12 is a common-mode circuit insertion loss simulation result of a filter circuit;

[0031] Figure 13 is a differential-mode circuit simulation principle diagram of a filter circuit;

[0032] Figure 14 is a differential-mode circuit insertion loss simulation result of a filter circuit. DETAILED DESCRIPTION

[0033] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0034] It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict; and all other embodiments obtained by those skilled in the art based on the embodiments in the present disclosure without creative labor, belong to the scope of protection of the present disclosure.

[0035] It is important to note that the various aspects described throughout this disclosure can be combined in a wide variety of ways. It should be apparent that aspects described herein can be implemented in various forms of hardware, software, or a combination thereof; and that the described aspects can be implemented differently depending on the particular desires of a user or designer, and particular implementations described herein are used as examples only. Further, any acts or event described can be implemented in the art's various forms, including hardware, software, or a combination thereof. Further, described methods can be implemented by one or more processors, either alone or in combination, particularly in a Society of Automotive Engineers (SAE) J1939 network, and each method does not necessarily need to be implemented by one specific processor. For example, a method can be implemented by one processor at a time, by one processor after another, by one processor or one processor core at a time and then another processor or another processor core at another time, etc. Further, steps or acts in a process described can not necessarily need to be implemented in the order described, unless otherwise imposed by the context.

[0036] The embodiment of the application is a ship low ground capacitance filter design method, the specific process is:

[0037] Step one, use inductance as the main filter device, for the low frequency band below 100 kHz, the magnetic core of inductance uses iron-based nanocrystalline material, for the low frequency band from 100 kHz to 1 MHz, the magnetic core of inductance uses MnZn magnetic material, for the high frequency band above 1 MHz, the magnetic core of inductance uses NiZn magnetic material;

[0038] Step two, based on the designed inductance, design a multi-stage filter circuit combining low frequency and high frequency;The filter circuit comprises: a plurality of common mode inductors connected in series, a differential mode capacitor Cx connected in parallel across the common mode inductor, a common mode capacitor Cy connected in parallel between the live line and the ground, and a common mode capacitor Cy connected in parallel between the zero line and the ground.

[0039] Step three, modular packaging and glue filling, so that the center position of the filter is at the center position of the shell, and no overall insulating glue filling is performed.

[0040] The following describes the principles / considered elements based on the design process of the embodiment of the application, as shown in Figure 1 The ship low ground capacitance filter design flow.

[0041] Further, in the embodiment, only inductance is used as the main filter device to achieve the beneficial effects of wide insertion loss frequency band and small filter ground capacitance.

[0042] The above design is on the one hand to meet the wideband filtering requirement, and on the other hand to reduce the filter ground capacitance, the entire filter circuit should not use common mode capacitor, i.e. functional ground capacitance, only inductance is used as the main filter device to achieve the beneficial effects of wide insertion loss frequency band and small filter ground capacitance.

[0043] Further, for the low frequency band below 100 kHz, the magnetic core of the inductor adopts iron-based nanocrystalline material, and for the low frequency band from 100 kHz to 1 MHz, the magnetic core of the inductor adopts MnZn magnetic material to realize the common mode filtering function, and the specific inductance value needs to be determined in combination with the insertion loss requirement of the frequency band.

[0044] In order to make the normal transmission signal in the passband as little affected as possible, the attenuation in the stopband needs to be large. The stopband of the Butterworth filter function presents the flattest characteristic, so the Butterworth filter function model is selected for the design of the passive low-pass filter circuit of the marine low-ground capacitance filter. 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 cutoff frequency, and n is the order of the filter (the number of L and C elements). Since the ground capacitance needs to be controlled, the use of capacitor devices should be reduced, and the filtering performance mainly relies on large inductance. Therefore, the inductor magnetic core needs to adopt amorphous, MnZn magnetic material with good low-frequency performance.

[0047] Due to the limitation of filter temperature rise and voltage drop, conventional differential mode inductors cannot be used to suppress low-frequency interference. Inductors with good performance and not easy to saturate in the frequency range below 100 kHz need to be selected, and simulation needs to be designed and verified to ensure that the insertion loss of the low-frequency band meets the requirements.

[0048] Further, for the high frequency band above 1 MHz, inductors with good high-frequency performance NiZn magnetic material as the magnetic core are used to realize the common mode filtering function, and the specific inductance value needs to be determined in combination with the insertion loss requirement of the frequency band.

[0049] Since the ground capacitance needs to be controlled, the use of capacitor devices should be reduced, and inductor devices with good suppression effect in the high frequency band need to be selected. High-frequency performance NiZn magnetic material is used to make common mode inductor components.

[0050] Further, the functional inductor device is modularly packaged and glued, and the arrangement method of placing the device in the center position of the shell parallel to the ground of the filter structure is used to meet the insulation and structural strength of the filter and realize the beneficial effect of small ground capacitance of the filter.

[0051] Because of the need to control the ground capacitance, the ground function capacitor cannot be used in the circuit design. But there is a distributed capacitance between the filter circuit and the filter shell, and at the same time the current of the filter is large (high power carrying capacity) and the wideband insertion loss requirement is high, resulting in a large size of the filter circuit, and the distributed capacitance of the filter circuit to the ground (filter shell) is also large. According to the definition of capacitance, two conductive plates close to each other, filled with dielectric material ε in between, constitute a capacitor. The calculation formula of the flat plate capacitor is shown in formula 2:

[0052]

[0053] Where: ε - dielectric constant (F / m); S - conductive plate area; d - distance between two conductive 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 conductive plate, the larger the capacitance;

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

[0058] Therefore, the main factors affecting the ground capacitance of the filter are:

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

[0060] (2) Related to whether to use insulating glue to encapsulate the filter circuit.

[0061] Finally, by controlling the ground function capacitor and not performing overall insulating glue encapsulation and other measures to control the ground distributed capacitance, the ground capacitance of the filter is ensured to meet the requirements.

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

[0063] Further, the filter shell is made of 316L stainless steel material, and the shielding body is made of surface conductive oxidation treated 2A12 hard aluminum to meet the corrosion resistance requirements of marine filters in high temperature and high humidity and other harsh environments. And continuous welding is used to meet the vibration resistance requirements of the filter structure.

[0064] The following will be described in detail taking a marine filter with a working frequency of 10 kHz-10 MHz and a ground capacitance of not more than 2nF as an example.

[0065] Step one, in the design of low frequency filter circuit 10kHz~100kHz, since the filter in 10k~100kHz frequency band, mainly involves the differential mode insertion loss, for this Butterworth filter function should be in differential mode circuit. To achieve the technical indicators of low frequency, the five order Butterworth filter function is adopted, the filter circuit has two common mode inductance and one differential mode inductance. As shown in Figure 2 , Cy is the common mode capacitance in the circuit, Lc1 and Lc2 are common mode inductance, Ld is differential mode inductance, Cx1 is differential mode capacitance.

[0066] According to the topology of common mode and differential mode circuit, the common mode and differential mode insertion loss of low frequency filter circuit is simulated. The common mode circuit parameters are shown in Figure 3 , the insertion loss is shown in Figure 4 ; the differential mode circuit parameters are shown in Figure 5 , the insertion loss result is shown in Figure 6 .

[0067] Step two, considering the voltage drop of the filter, the topology of high frequency filter circuit is similar to that of low frequency circuit, which is also composed of high frequency common mode inductance and common mode and differential mode capacitance. The difference lies in that the common mode insertion loss of high frequency is more closely related to common mode capacitance. Since the ground capacitance needs to be controlled, the use of capacitor devices should be reduced, and inductance devices with good suppression effect in high frequency band should be selected. NiZn ferrite has low permeability and high resistance, which is suitable for high frequency occasions. NiZn ferrite can be used in the frequency range of 1MHz to 300MHz, and its main features are low permeability, high resistivity and small high frequency eddy current loss. It is the best inductance magnetic core material in MHz high frequency band. Therefore, NiZn magnetic material with good high frequency performance is adopted to make common mode inductance components. In order to avoid magnetic saturation, high frequency inductance still adopts common mode inductance form. Considering the actual power requirement, NiZn common mode inductance adopts circular ring magnetic core. Since the common mode inductance with large current has large volume, it will increase the distributed capacitance of the filter circuit to the ground. Therefore, appropriate differential mode capacitance is adopted to realize large differential mode capacitance through parallel connection, and then the volume of common mode inductance is reduced.

[0068] Step three, in the design of the foregoing filter circuit, the limitation of the ground function capacitance of the filter has been considered. Further, the control of the ground capacitance of the filter circuit focuses on the control of the distributed capacitance of the filter circuit to the ground. The ground capacitance is further controlled through the internal component arrangement and packaging design of the filter.

[0069] In this example, the filter shell is made of metal material to ensure the structure 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 shell (the other electrode). In the filter circuit, only the inductance is a conductive body. Therefore, the determining factor of the filter circuit electrode is the inductance.

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

[0071] Taking two filter circuits as shown in Figure 8 , Figure 9 , relative to Cy2 of the bottom surface of the filter shell, the areas of the inductive elements projected on the bottom surface are different, and thus are different. Obviously, the inductive element ring in the filter circuit is placed vertically to the ground, and the S formed with the ground is smaller, and the distributed capacitance formed is 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. Therefore, 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 as small as possible. Therefore, the volume of the filter circuit must be as small as possible, and new structures that reduce the distributed capacitance must be used.

[0073] On the other hand, in order to optimize the ε parameter in formula (2), the traditional filter usually fills the gap between the filter circuit and the metal shell with potting material to fix the filter circuit and increase the insulation strength. However, as can be seen from formula (2), since the ε of the potting material is greater than that of air, potting will inevitably increase the distributed capacitance. Therefore, 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 circuit after cascading the low-frequency and high-frequency filter circuits finally forms the following complete filter circuit design scheme: composed of "two-stage common mode (low frequency)" + one-stage common mode (high frequency), the circuit schematic diagram is as shown in Figure 10 , the common mode and differential mode circuit simulation parameters and insertion loss of the filter circuit are as shown in Figure 11-14 , wherein:

[0075] Common mode inductor Lc1: made of iron-based nanocrystalline material to realize 10k-100kHz low frequency high insertion loss and small volume, and lay the necessary foundation for the realization of extremely low distributed capacitance of the filter;

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

[0077] Common mode inductance Lc3: using NiZn ferrite material, realizing 10M-100MHz high frequency insertion loss.

[0078] The circuit design of the whole filter is based on electromagnetic simulation, and the performance of the sample can meet the design index of insertion loss, and there is enough margin. The parameters of the filter are as follows: common mode inductance Lc1 inductance: 30mH; common mode inductance Lc2 inductance: 3mH; common mode inductance Lc3 inductance: 50uH; common mode capacitance Cy capacitance: 0.23nF; differential mode capacitance Cx capacitance: 10uF. From the above circuit parameters, it can be seen that the capacitance value of each line to ground capacitance of the alternating current filtering circuit is only 0.23nF.

[0079] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A design method for a marine low-to-ground capacitance filter, characterized in that, The specific process is as follows: First, inductors are used as filtering devices. For the low frequency band below 100kHz, the inductor core is made of iron-based nanocrystalline material. For the low frequency band from 100kHz to 1MHz, the inductor core is made of MnZn magnetic material. For the high frequency band above 1MHz, the inductor core is made of NiZn magnetic material. Furthermore, based on the designed inductor, a multi-stage filter circuit combining low-frequency and high-frequency filtering is designed. The filtering circuit includes: multiple common-mode inductors connected in series, a differential-mode capacitor Cx connected in parallel across the common-mode inductors, a common-mode capacitor Cy connected in parallel between the live wire and ground, and a common-mode capacitor Cy connected in parallel between the neutral wire and ground. The filter circuit includes two stages of low-frequency common-mode inductors Lc1 and Lc2 and one stage of high-frequency common-mode inductor Lc3, with the three inductors cascaded together. Common-mode inductor Lc1 is made of iron-based nanocrystalline material, common-mode inductor Lc2 is made of low-permeability MnZn ferrite material, and common-mode inductor Lc3 is made of NiZn ferrite material. The inductor element rings in the filter circuit are placed perpendicular to the ground. The differential mode capacitor Cx connected in parallel across the common mode inductor consists of three capacitors, and a protection resistor is connected in parallel across each differential mode capacitor Cx. Finally, modular encapsulation and potting are performed so that the inductance of the filter circuit is parallel to the casing, the center of the filter circuit is located at the center of the casing, and no overall insulating potting is performed.

2. The design method for a marine low-to-ground capacitance filter according to claim 1, characterized in that, The NiZn common-mode inductor uses a toroidal magnetic core.

3. The design method for a marine low-to-ground capacitance filter according to claim 1, characterized in that, The filter housing is made of stainless steel, and the surface is made of conductive anodized aluminum to form the shield.

4. The design method for a marine low-to-ground capacitance filter according to claim 1, characterized in that, The common-mode inductor Lc1 has an inductance of 30mH; the common-mode inductor Lc2 has an inductance of 3mH; the common-mode inductor Lc3 has an inductance of 50uH; the common-mode capacitor Cy has a capacitance of 0.23nF; and the differential-mode capacitor Cx has a capacitance of 10uF.

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