Design method for space electromagnetic radiation of brushless direct current motor

Abstract

The invention provides a direct current brushless motor space electromagnetic radiation design method, which relates to the field of space electromagnetic radiation, and comprises the following steps: dividing a controller function module into an interference filtering module, a BOOST circuit module, an auxiliary power supply module, a driving module, a power module, a control module and a user operation module; the interference filtering and BOOST circuit module is arranged in a first partition, the auxiliary power supply and the driving and power module are arranged in a second partition, the control module is arranged in a third partition, and the user operation module is arranged in a fourth partition; a multi-layer printed circuit board is adopted, and two middle layers are a power supply layer and a ground layer; the partitions are physically isolated by metal compartments; a metal tower with a boss and a conductive sealing ring is arranged at a three-phase line interface of the motor, and the boss is embedded into a concave hole of a controller shell to be pressurized and sealed; each module is provided with an independent grounding terminal; a semi-annular metal shielding cover is arranged on the inner wall of the controller shell; a harmonic spectrum is collected in real time and a switching frequency is dynamically optimized, so that a harmonic component falls below a shielding cut-off frequency band.

Description

Technical Field

[0001] The present invention relates to the field of space electromagnetic radiation, in particular to a design method for space electromagnetic radiation of a brushless DC motor. Background Art

[0002] Brushless DC motors (BLDCs), due to their high efficiency, low noise, and long life, are widely used in industrial automation, electric vehicles, and household appliances. With the increasing integration of electronic devices and the prevalence of wireless communication technology, the problem of electromagnetic radiation generated by motor controllers has become increasingly prominent. This radiation primarily originates from the high-speed switching action of power modules (such as PWM control), high-frequency circuit crosstalk, and common-mode current leakage in the motor phase lines. Its spectrum ranges from 30MHz to 1GHz, causing severe interference to surrounding precision electronic equipment (such as communication terminals and medical equipment), and even triggering safety limits for human electromagnetic exposure.

[0003] The industry currently generally adopts solutions such as overall metal shell shielding, adding filtering circuits, or optimizing grounding paths to suppress radiation. However, overall shielding solutions significantly increase size and cost, and it is difficult to solve the problem of high-frequency harmonics leaking through connector gaps within the controller. While filtering circuits can attenuate interference in specific frequency bands, their effectiveness is limited when dealing with broadband harmonics (such as odd harmonics of the PWM switching frequency), and they also introduce additional power consumption. Improper grounding design can lead to ground loop coupling, which in turn amplifies common-mode radiation. More critically, traditional static design methods cannot dynamically respond to spectrum shifts caused by changes in motor load, causing some harmonic components to exceed the effective cutoff frequency band of the shielding structure.

[0004] Furthermore, the high-density integration of multiple modules causes cross-interference: the high-frequency oscillations of the BOOST circuit and the rapid switching of the driver module are coupled through the common power supply layer, generating superimposed radiation. The waveguide effect formed by the structural assembly tolerances of the motor's three-phase line interface becomes the main source of radiation in the 30-300MHz frequency band. Existing technologies lack a quantitative adaptive design for waveguide size and switching frequency, nor a mathematical relationship between partition layout spacing and interference wavelength, resulting in a reliance on empirical debugging for suppression effectiveness. The conflict between heat dissipation requirements and electromagnetic shielding further exacerbates design difficulties. Failure to coordinately optimize the geometric parameters of the metal compartments will affect heat conduction and weaken isolation performance. Summary of the Invention

[0005] In order to solve the technical problems of high-frequency conduction radiation leakage, insufficient dynamic suppression of broadband harmonics, multi-module crosstalk superposition radiation and grounding heat dissipation design conflicts in the existing technology, the present invention provides a design method for the spatial electromagnetic radiation of a brushless DC motor.

[0006] The technical solutions provided by the present invention are as follows:

[0007] The present invention provides a method for designing spatial electromagnetic radiation of a brushless DC motor, comprising:

[0008] The controller functional modules are divided into interference filtering module, BOOST circuit module, auxiliary power supply module, drive module, power module, control module and user operation module;

[0009] The interference filtering module and the BOOST circuit module are arranged in the first partition, the auxiliary power supply module, the drive module and the power module are arranged in the second partition, the control module is arranged in the third partition, and the user operation module is arranged in the fourth partition;

[0010] Use a multi-layer PCB layout, with the middle two layers being the power layer and the ground layer;

[0011] Each partition is physically separated by metal compartments;

[0012] A metal tower is provided at the interface between the motor U / V / W three-phase wires and the controller, wherein the tower has a boss and a conductive sealing ring;

[0013] The boss is embedded in the concave hole of the controller metal shell and pressurized and sealed;

[0014] Set up independent grounding terminal for each functional module;

[0015] Constructing a semi-circular metal shielding cover on the inner wall of the controller housing;

[0016] The PWM harmonic spectrum of the motor is collected when it is running, and the switching frequency is dynamically optimized to make the main harmonic components fall below the shielding cutoff frequency band.

[0017] Furthermore, the height of the metal compartment is more than twice the thickness of the PCB, and the spacing D between the partitions satisfies:

[0018] D≥(0.25+0.05log 10 f max )·λ min

[0019] where f max is the maximum operating frequency of the system, λ min is the wavelength of minimum interference.

[0020] Furthermore, the boss length satisfies:

[0021]

[0022] Where c is the speed of light, f sw is the PWM switching frequency, ε r The dielectric constant of the sealing ring, and the sealing pressure ≥ 5N / cm 2 Make the deformation rate ≥30%.

[0023] Furthermore, the dielectric constant ε r By adjusting the conductive filler density, the density is controlled within the range of 2.0-5.0.

[0024] Furthermore, the grounding copper foil line width is determined according to the maximum operating current of the module, the copper foil current density and the temperature derating factor, wherein the temperature derating factor decays exponentially with increasing ambient temperature.

[0025] Furthermore, a windowed FFT algorithm is used to calculate the harmonic distortion THD. When THD>5% or the switching frequency is lower than 2 times the cutoff frequency, the switching frequency is dynamically updated using a gradient descent algorithm.

[0026] Furthermore, the thickness t of the dielectric layer between the power layer and the ground layer satisfies

[0027]

[0028] where λ min is the minimum interference wavelength, ε PCB is the dielectric constant of the PCB substrate.

[0029] Furthermore, the curvature radius of the semi-annular shield is greater than 1 / 2 of the maximum physical size of the radiation source, and the radiation attenuation is made ≥40dB through three-dimensional electromagnetic simulation optimization.

[0030] Furthermore, when there are ≥3 wireless communication base stations in the controller working environment, the base station application scenario is triggered, and a fully sealed metal shell is added in the base station application scenario, and its thickness meets the shielding effectiveness ≥50+20·log 10 (target frequency × material conductivity × thickness).

[0031] Furthermore, the cutoff frequency of the metal tower is inversely proportional to the length of the boss, and the switching frequency after optimization is more than 1.2 times the cutoff frequency.

[0032] The beneficial effects brought about by the technical solution provided by the present invention include at least:

[0033] (1) In this invention, a waveguide window-type metal tower and a conductive sealing ring are combined to completely seal the gaps at the motor's three-phase line interface by precisely controlling the boss length and applying high-pressure sealing. This design utilizes the waveguide cutoff principle to confine high-frequency electromagnetic interference within the shielded cavity, effectively resolving the broadband radiation leakage problem at the interface in traditional solutions and significantly reducing electromagnetic emissions in the 30 to 300 MHz frequency band.

[0034] (2) In this invention, based on the real-time acquisition of the motor harmonic spectrum, combined with fast Fourier transform analysis and gradient descent optimization algorithms, the switching frequency is automatically adjusted to ensure that the main harmonic components are always below the effective cutoff frequency band of the shielding structure. This technology breaks through the limitations of static design and dynamically adapts to the spectrum shift caused by load changes, blocking broadband harmonic radiation at the source.

[0035] (3) In the present invention, the electromagnetic coupling path between highly sensitive modules is blocked by quantifying the partition spacing standard and the physical isolation design of the metal compartment; at the same time, the semi-annular shielding cover and the independent grounding terminal form a local electromagnetic enclosure, and the heat-conductive filling material is used to achieve a balance between heat dissipation and electromagnetic compatibility performance, fundamentally solving the problem of the conflict between radiation superposition and thermal management in high-density integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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 creative work.

[0037] Figure 1 A schematic flow chart of a method for designing spatial electromagnetic radiation of a brushless DC motor provided by an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of the system architecture of a method for designing spatial electromagnetic radiation of a brushless DC motor provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0040] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as an "exemplary" in the present invention should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of the word "exemplary" is intended to present concepts in a concrete manner. Furthermore, in the embodiments of the present invention, "and / or" can mean both or either of the two.

[0041] In the embodiments of the present invention, the terms "image" and "picture" may be used interchangeably. It should be noted that, when the distinction between them is not emphasized, their intended meanings are the same. The terms "of," "corresponding," and "corresponding" may be used interchangeably. It should be noted that, when the distinction between them is not emphasized, their intended meanings are the same.

[0042] In the embodiments of the present invention, sometimes a subscript such as W1 may be mistakenly written as a non-subscript form such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0043] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0044] Reference Manual Figure 1 , which shows a flow chart of a method for designing spatial electromagnetic radiation of a brushless DC motor provided by an embodiment of the present invention.

[0045] An embodiment of the present invention provides a method for designing the spatial electromagnetic radiation of a brushless DC motor. The process may include the following steps:

[0046] The process begins with hierarchical partitioning: dividing the four functional modules into zones, laying out the power and ground planes of the printed circuit board, and isolating the zones with metal compartments. Waveguide shielding design then begins: installing metal towers and pressurizing and sealing the bosses. Gradient grounding design follows: providing independent grounding terminals for each module and constructing a semi-circular shielding cover on the inner wall of the enclosure. The dynamic spectrum tuning phase then begins: collecting the pulse width modulation harmonic spectrum and calculating the harmonic distortion. If the harmonic distortion is greater than 5% or the switching frequency is less than twice the cutoff frequency, the switching frequency is optimized using a gradient descent algorithm; otherwise, the process terminates. After optimization, a determination is made as to whether the harmonics fall below the cutoff frequency band. If not, the process returns to the spectrum tuning step for re-collection and analysis. If so, the radiation meets the standard, and the process concludes.

[0047] like Figure 2 As shown, the controller's functional modules are divided into four sections: the first section contains the interference filtering module and the boost circuit module; the second section contains the auxiliary power supply module, the drive module, and the power module; the third section is the independent control module; and the fourth section is the user operation module. Each section is physically isolated by metal compartments. The printed circuit board adopts a multi-layer structure, with the middle two layers being the power supply layer and the ground layer, and the top and bottom layers being used for signal wiring. A metal tower with a boss and a conductive sealing ring is installed at the three-phase line interface of the motor. The boss is embedded in the recess of the controller's metal casing. A semi-circular metal shield is constructed on the inner wall of the controller casing. Each functional module is connected to the main ground point in a star topology via independent ground terminals.

[0048] Specifically, a hierarchical partition design is first performed to divide the functional modules of the brushless DC motor controller into seven parts: interference filtering module, BOOST circuit module, auxiliary power supply module, drive module, power module, control module and user operation module. Among them, the interference filtering module and the BOOST circuit module are jointly arranged in the first partition, the auxiliary power supply module, the drive module and the power module are arranged in the second partition, the control module is arranged separately in the third partition, and the user operation module is arranged in the fourth partition. A four-layer or multi-layer printed circuit board (PCB) is used to implement the layout, with the middle two layers serving as the power layer and the ground layer respectively, and the top and bottom layers are specifically used for arranging signal lines. Physical isolation is achieved between the partitions by metal partitions, which are made of aluminum alloy material and whose height is set to 2.5 times the thickness of the PCB. The spacing between the partitions is calculated and determined based on the system's maximum operating frequency and the minimum interference wavelength, and specifically satisfies the relationship: partition spacing D≥(0.25+0.05log 10 f max )·λ min , where f max By analyzing the controller clock frequency and the power device switching frequency and taking the maximum value, λ min By formula λ min =c / f max Calculation, c is the speed of light (3×10 8 m / s).

[0049] A waveguide cutoff shielding design is implemented at the interface between the motor U / V / W three-phase line and the controller. A waveguide window-type metal tower is made of 6061 aluminum alloy. The tower base and the long-side rectangular boss are integrally formed using CNC machine tools. The boss length L must meet where f sw is the pulse width modulation (PWM) switching frequency, and the initial value is set to 15kHz according to the rated power of the motor. r The dielectric constant of the conductive sealing ring is 0.05mm. The boss surface turning accuracy is controlled within ±0.05mm, and the conductive silicone rubber sealing ring (Shore hardness 70A) is applied by hydraulic equipment at 6N / cm 2 The pressure is embedded in the concave hole of the cast aluminum housing of the controller, causing the sealing ring to produce a 35% deformation rate. The dielectric constant of the conductive sealing ring is ε r By adjusting the density of the silver-coated copper powder filler to be controlled within the range of 3.2-4.5, the filler density ρ is 150g / cm 3 Prepared to ensure surface impedance ≤ 0.08Ω.

[0050] During the gradient grounding design phase, each functional module is equipped with an independent grounding terminal. 2oz copper foil is used to make the grounding line, with a line width of w g According to the maximum operating current of the module Imax , copper foil current density J and temperature derating factor k. The temperature derating factor k changes with the ambient temperature T and satisfies When the ambient temperature is 40℃, K is set to 0.63. A semi-circular copper-nickel alloy shielding cover (conductivity 1.6×10 7 The shield's curvature radius, R, was optimized using 3D electromagnetic simulation software to 0.55 times the maximum physical size of the radiation source, with radiation attenuation set at 45dB. Finite element analysis software was used to establish an electromagnetic model of the motor controller, and the curvature radius was adjusted to meet the radiation attenuation standard in the 30-100MHz frequency band.

[0051] The dynamic spectrum tuning process uses a digital signal processor (DSP) to collect the PWM harmonic spectrum of the motor in real time during operation. First, the 1024-point Fast Fourier Transform (FFT) algorithm with a Blackman-Harris window function is used to calculate the total harmonic distortion (THD). The sampling frequency is set to 10 times the switching frequency. When THD>5% or the switching frequency f is detected, the sw <2f c (f c When the metal tower cutoff frequency is reached, the gradient descent algorithm is started to optimize the switching frequency. The objective function is defined as J = |THD-5%| + max(0,2f c -f sw ), the step size η is set to 0.01, and the iterative update formula is Until THD≤4.8% and f sw ≥1.25f c .

[0052] The thickness of the dielectric layer between the power layer and the ground layer must be strictly controlled to meet where ε PCB Take the dielectric constant of FR4 substrate as 4.5, λ min The wavelength corresponding to 1GHz is 30mm, and the dielectric layer thickness is designed to be 0.25mm. In the base station application scenario, an additional cold-rolled steel plate fully sealed metal shell is added, and the thickness t is calculated according to the shielding effectiveness formula SE≥50+20·log 10 The target suppression frequency is 800 MHz and the material conductivity is 1.03×10 7 S / m, the final thickness is designed to be 1.2mm. Laser welding is used during installation to ensure the airtightness of the joints, and conductive epoxy resin is coated on the inner wall of the shell to enhance the overlap. The cutoff frequency f of the metal tower c Inversely proportional to the boss length L, satisfying Optimized switching frequency f sw Set to 1.3f c , ensuring that the main harmonic components are below the cutoff frequency band.

[0053] When arranging modules in zones, the minimum spacing between the first and second zones is set at 12mm, and the third zone maintains a 15mm spacing with the other zones. The power module ground terminals are connected to the main ground point in a star topology, with a grounding copper foil width of 3.5mm. Before installing the conductive seal, clean the contact surface with isopropyl alcohol. After pressurization and sealing, measure the interface shielding effectiveness with a network analyzer to ensure attenuation greater than 30dB in the frequency band above 300MHz. During dynamic frequency modulation, the DSP performs spectrum analysis every 100ms, and the gradient descent algorithm is limited to 50 iterations for convergence. The semi-circular shielding can has an opening angle of 110°, and the edges are curled to reduce edge radiation. The ventilation holes in the base station casing utilize a waveguide array design with an aperture diameter less than 3mm and a depth greater than 15mm to suppress high-frequency electromagnetic leakage. A low dissipation factor (Df ≤ 0.02) substrate is used during PCB lamination, and the power plane is divided into multiple independent zones to reduce crosstalk. Thermally conductive silicone pads are placed between each metal compartment and the PCB to ensure both thermal management and enhanced electromagnetic isolation. During the three-dimensional electromagnetic simulation optimization, the focus was on analyzing the hotspot radiation areas of the power module field-effect transistor and freewheeling diode, and adjusting the curvature of the shield to reduce the near-field magnetic field intensity to below 15dBμA / m.

[0054] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0055] (1) In this invention, a waveguide window-type metal tower and a conductive sealing ring are combined to completely seal the gaps at the motor's three-phase line interface by precisely controlling the boss length and applying high-pressure sealing. This design utilizes the waveguide cutoff principle to confine high-frequency electromagnetic interference within the shielded cavity, effectively resolving the broadband radiation leakage problem at the interface in traditional solutions and significantly reducing electromagnetic emissions in the 30 to 300 MHz frequency band.

[0056] (2) In this invention, based on the real-time acquisition of the motor harmonic spectrum, combined with fast Fourier transform analysis and gradient descent optimization algorithms, the switching frequency is automatically adjusted to ensure that the main harmonic components are always below the effective cutoff frequency band of the shielding structure. This technology breaks through the limitations of static design and dynamically adapts to the spectrum shift caused by load changes, blocking broadband harmonic radiation at the source.

[0057] (3) In the present invention, the electromagnetic coupling path between highly sensitive modules is blocked by quantifying the partition spacing standard and the physical isolation design of the metal compartment; at the same time, the semi-annular shielding cover and the independent grounding terminal form a local electromagnetic enclosure, and the heat-conductive filling material is used to achieve a balance between heat dissipation and electromagnetic compatibility performance, fundamentally solving the problem of the conflict between radiation superposition and thermal management in high-density integration.

[0058] The above content is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

[0059] There are a few points to note:

[0060] (1) The drawings of the embodiments of the present invention only relate to the structures related to the embodiments of the present invention. Other structures may refer to conventional designs.

[0061] (2) For the sake of clarity, the thickness of layers or regions in the drawings used to describe the embodiments of the present invention are exaggerated or reduced, that is, these drawings are not drawn to scale. It is understood that when an element such as a layer, film, region, or substrate is referred to as being "on" or "under" another element, the element may be "directly" "on" or "under" the other element or intervening elements may be present.

[0062] (3) In the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other to form new embodiments.

[0063] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A design method for the spatial electromagnetic radiation of a brushless DC motor, characterized in that: include: The controller functional modules are divided into interference filtering module, BOOST circuit module, auxiliary power supply module, drive module, power module, control module and user operation module; The interference filtering module and the BOOST circuit module are arranged in the first partition, the auxiliary power supply module, the drive module and the power module are arranged in the second partition, the control module is arranged in the third partition, and the user operation module is arranged in the fourth partition; Use a multi-layer PCB layout, with the middle two layers being the power layer and the ground layer; Each partition is physically separated by metal compartments; A metal tower is provided at the interface between the motor U / V / W three-phase wires and the controller, wherein the tower has a boss and a conductive sealing ring; The boss is embedded in the concave hole of the controller metal shell and pressurized and sealed; Set up independent grounding terminal for each functional module; Constructing a semi-circular metal shielding cover on the inner wall of the controller housing; The PWM harmonic spectrum of the motor is collected when it is running, and the switching frequency is dynamically optimized to make the main harmonic components fall below the shielding cutoff frequency band.

2. The method for designing the spatial electromagnetic radiation of a brushless DC motor according to claim 1, characterized in that: include: The height of the metal compartment is more than twice the thickness of the PCB, and the spacing D between the partitions meets the following requirements: D≥(0.25+0.05log 10 f max )·l min where f max is the maximum operating frequency of the system, λ min is the wavelength of minimum interference.

3. The method for designing the spatial electromagnetic radiation of a brushless DC motor according to claim 1, characterized in that: include: The boss length satisfies: Where c is the speed of light, f sw is the PWM switching frequency, ε r The dielectric constant of the sealing ring, and the sealing pressure ≥ 5N / cm 2 Make the deformation rate ≥30%.

4. The method for designing the spatial electromagnetic radiation of a brushless DC motor according to claim 3, characterized in that: include: The dielectric constant ε r By adjusting the conductive filler density, the density is controlled within the range of 2.0-5.

0.

5. The method for designing the spatial electromagnetic radiation of a brushless DC motor according to claim 1, characterized in that: include: The grounding copper foil line width is determined based on the maximum operating current of the module, the copper foil current density, and the temperature derating factor. The temperature derating factor decays exponentially with increasing ambient temperature.

6. The method for designing the spatial electromagnetic radiation of a brushless DC motor according to claim 1, characterized in that: include: The windowed FFT algorithm is used to calculate the harmonic distortion rate THD. When THD>5% or the switching frequency is lower than 2 times the cutoff frequency, the switching frequency is dynamically updated using the gradient descent algorithm.

7. The method for designing the spatial electromagnetic radiation of a brushless DC motor according to claim 1, characterized in that: include: The thickness t of the dielectric layer between the power layer and the ground layer satisfies where λ min is the minimum interference wavelength, ε PCB is the dielectric constant of the PCB substrate.

8. The method for designing the spatial electromagnetic radiation of a brushless DC motor according to claim 1, characterized in that: include: The curvature radius of the semi-annular shield is greater than 1 / 2 of the maximum physical size of the radiation source, and the radiation attenuation is made ≥40dB through three-dimensional electromagnetic simulation optimization.

9. The method for designing the spatial electromagnetic radiation of a brushless DC motor according to claim 1, characterized in that: include: In base station applications, a fully sealed metal shell is added, and its thickness meets the shielding effectiveness ≥ 50+20·log 10 (target frequency × material conductivity × thickness).

10. The method for designing the spatial electromagnetic radiation of a brushless DC motor according to claim 6, characterized in that: include: The cutoff frequency of the metal tower is inversely proportional to the length of the boss, and the switching frequency after optimization is more than 1.2 times the cutoff frequency.

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