Broadband high-voltage DC block design method suitable for power electronic equipment and DC block

Abstract

The invention provides a broadband high-voltage DC block design method suitable for power electronic equipment and a DC block. The design method is characterized by comprising the following steps: step 1, designing a coaxial transmission line structure suitable for a high-voltage environment according to the relation between the characteristic impedance of a coaxial cable and the radiuses of inner and outer conductors and considering the breakdown voltage of a medium between the conductors; 2, according to the measurement frequency range of the power electronic equipment, the withstand voltage and the capacitance value of a blocking capacitor are designed, so that the S parameter of the blocking capacitor meets the performance requirement; and step 3, designing an interface adapter according to requirements. The DC block designed by the invention can greatly attenuate low-frequency high-voltage large-current components in the power electronic equipment, and meanwhile, ensures that a measurement signal is loaded on the tested equipment without distortion, so that the DC block is suitable for a power electronic equipment test environment. According to the invention, the requirements on the dielectric material and the processing precision of the DC block are low, the design method has certain universality, the device is simple in structure, and the manufacturing method is easy to implement.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic compatibility measurement, specifically to a design method and a DC blocker suitable for power electronic equipment. Background Technology

[0002] A DC blocker is a radio frequency (RF) connection device that functions similarly to a high-pass filter. It blocks DC and low-frequency signals from passing through without affecting the transmission of RF signals. DC blockers have advantages such as wide operating bandwidth and low insertion loss, and are commonly used in electronic measuring instruments for DC protection to prevent damage to sensitive RF components and instruments caused by DC voltage or current.

[0003] However, existing DC blockers have a low withstand voltage range, poor applicability in high-voltage environments, and an excessively high operating frequency range, resulting in poor performance when applied to power electronic equipment. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, the first objective of this invention is to provide a design method for a broadband high-voltage DC blocker suitable for power electronic equipment testing environments, characterized by comprising the following steps:

[0006] Step 1: Based on the relationship between the characteristic impedance of the coaxial cable and the radii of its inner and outer conductors, and considering the breakdown voltage of the dielectric between the conductors, design a coaxial transmission line structure suitable for high-voltage environments.

[0007] Step 2: Based on the measurement frequency range of the power electronic equipment, design the withstand voltage and capacitance value of the DC blocking capacitor so that the S-parameters of the DC blocking capacitor meet the performance requirements.

[0008] Step 3: Design the interface adapter according to the requirements.

[0009] The second objective of this invention is to provide a broadband high-voltage DC blocker suitable for power electronic equipment, which is obtained through the above-described design method. It includes a DC blocking capacitor 1, a coaxial cable, an RF connector 4, and a metal housing 5. The coaxial cable includes an inner metal conductor 2 and an outer metal conductor 3. One end of the inner metal conductor 2 has a tapered structure and is connected to the RF connector 4, while the other end is connected to the DC blocking capacitor 1. The outer metal conductor 3 has a hollow cylindrical structure to enclose the inner metal conductor 2. The metal housing 5 is used to fix the inner metal conductor 2, the outer metal conductor 3, and the RF connector 4.

[0010] This invention solves the technical problem that existing DC blockers are difficult to apply to the testing environment of power electronic equipment. It also has low requirements for the dielectric material and processing precision of the DC blocker, the design method has a certain degree of universality, and the device structure is simple and the manufacturing method is easy to implement. Attached Figure Description

[0011] Figure 1 This is a flowchart illustrating a broadband high-voltage DC blocking device design method suitable for power electronic equipment proposed in Embodiment 1 of the present invention.

[0012] Figure 2 S is the coaxial cable of the embodiment of the present invention. 11 Parameter curves;

[0013] Figure 3 S is the coaxial cable of the embodiment of the present invention. 12 Parameter curves;

[0014] Figure 4 S is the broadband high-voltage DC blocking device in an embodiment of the present invention. 12 Parameter curves;

[0015] Figure 5 This is a schematic diagram of a broadband high-voltage DC blocking device suitable for power electronic equipment, as proposed in Embodiment 2 of the present invention. Detailed Implementation

[0016] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings. Additional aspects and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

[0018] Figure 1 This is a flowchart illustrating a broadband high-voltage DC blocker design method suitable for power electronic equipment proposed in Embodiment 1 of the present invention. Figure 1 As shown, the design method of a broadband high-voltage DC blocker suitable for power electronic equipment according to the present invention includes the following steps:

[0019] Step 101: Based on the relationship between the characteristic impedance of the coaxial cable and the radii of its inner and outer conductors, and considering the breakdown voltage of the dielectric between the conductors, design a coaxial transmission line structure suitable for high-voltage environments.

[0020] Step 102: Based on the measurement frequency range of the power electronic equipment, design the withstand voltage and capacitance value of the DC blocking capacitor so that the S-parameters of the DC blocking capacitor meet the performance requirements.

[0021] Step 103: Design the interface adapter according to the requirements.

[0022] Optionally, in one embodiment of the present invention, based on the relationship between the characteristic impedance of the coaxial cable and the radii of its inner and outer conductors, and considering the breakdown voltage of the dielectric between the conductors, a coaxial transmission line structure suitable for high-voltage environments is designed. Specifically, this is based on the resistance R0, inductance L0, conductance G0, and capacitance C0 per unit length of the coaxial cable.

[0023]

[0024] Its characteristic impedance Z can be obtained. C The relationship between the inner and outer conductor radii r1 and r2 is expressed as:

[0025]

[0026] j is the unit imaginary number, and ω is the angular frequency. To achieve 50Ω impedance matching, let the imaginary part of the characteristic impedance be 0 and the real part be 50Ω. Then the above relationship can be further simplified to:

[0027]

[0028] Where σ1 represents the conductivity of the coaxial cable conductor, d represents the penetration depth of the coaxial cable conductor, μ represents the permeability of the coaxial cable conductor, σ2 represents the conductivity of the intermediate medium of the coaxial cable, and ε represents the dielectric constant of the intermediate medium of the coaxial cable.

[0029] To prevent dielectric breakdown caused by excessively small spacing between the inner and outer conductors of the coaxial cable, the breakdown voltage of the dielectric must also be considered in the design. When the dielectric is gas, according to the Paschen curve formula:

[0030] V +bd =2.7pd1 0.8 (kV)

[0031] Another constraint that can be obtained for the radii of the inner and outer conductors of a coaxial cable is:

[0032]

[0033] Among them, V +bd The breakdown voltage is represented by d1, the distance between the outer surfaces of the inner and outer conductors is represented by d1 (mm), and the gas pressure is represented by p (atm). f s V represents the safety factor. bias This indicates the DC bias voltage for the operation of power electronic equipment, expressed in kV.

[0034] Based on the above two design requirements, the inner and outer conductor radii of the coaxial cable were calculated, and the parameters were optimized using the Smith chart, ultimately resulting in a coaxial transmission line structure suitable for high voltage.

[0035] Figure 2 , Figure 3 S is the coaxial cable of the embodiment of the present invention. 11 S 12 Parameter curves, such as Figure 2 and Figure 3 As shown, the coaxial cable designed according to the above method has an S value within the measurement frequency range of power electronic equipment, namely the 150kHz-30MHz / 108MHz band. 12 <-0.0007dB, measurement signals from power electronic devices can pass through coaxial cables without attenuation. 11 This refers to the reflection coefficient of port one when port two is matched, S 12 It refers to the reverse transmission coefficient from port 2 to port 1 when port 1 is matched.

[0036] Optionally, in one embodiment of the present invention, the withstand voltage and capacitance of the DC blocking capacitor are designed according to the measurement frequency range of the power electronic device so that the S-parameters of the DC blocking device meet the performance requirements. Specifically, since the coaxial cable does not affect the magnitude of the S-parameters of the DC blocking device under the condition of meeting 50Ω impedance matching, the S-parameters of the DC blocking device depend on the DC blocking capacitor.

[0037] According to the normalized impedance of the DC blocking capacitor, The corresponding S-parameter matrix S is represented as follows:

[0038]

[0039] For the normalized impedance, S Blk Let S be the S-parameters of the two-port network corresponding to the DC blocking capacitor, where j is the unit imaginary number, ω is the angular frequency, and C is the capacitance of the DC blocking capacitor. To ensure that the measurement signals from the power electronic equipment can pass completely through the DC blocker and that low-frequency signals are sufficiently attenuated, the above S-parameter matrix must satisfy the following conditions based on the required measurement frequency range: 12 The cutoff frequency of the curve is less than 150kHz, and the frequency S is below 50kHz. 12 Less than -40dB, which means the following:

[0040]

[0041] S 12 (dB)| f＝50Hz ≈20lg(2πC·10 6 <-40dB

[0042] Among them, f C S represents 12 The cutoff frequency of the curve, S 12 (dB)| f＝50Hz S represents 12The curve shows the decibel value at a frequency f equal to 50 Hz.

[0043] The estimated value of the DC blocking capacitor can be obtained by solving:

[0044] 9nF < C < 318nF

[0045] nF is an international unit representing the capacitance. At the same time, the withstand voltage of the DC blocking capacitor should be greater than the DC bias voltage of the power electronic equipment to ensure that the DC blocking capacitor can be used in the high voltage and high current environment of the equipment.

[0046] Figure 4 S is the broadband high-voltage DC blocking device in an embodiment of the present invention. 12 Parameter curves, such as Figure 4 As shown, only the 10nF DC blocking capacitor simultaneously satisfies the requirement at frequencies above 150kHz. 12 >-3dB, at frequencies below 50Hz 12 <-40dB, meets design requirements.

[0047] To achieve the above embodiments, the present invention also proposes a wideband high-voltage DC blocker suitable for power electronic equipment.

[0048] Figure 5 This is a schematic diagram of a broadband high-voltage DC blocker suitable for power electronic equipment, as proposed in Embodiment 2 of the present invention. Figure 5 As shown, this broadband high-voltage DC blocker suitable for power electronic equipment includes a DC blocking capacitor 1, a coaxial cable, an RF connector 4, and a metal housing 5. The coaxial cable includes an inner metal conductor 2 and an outer metal conductor 3. One end of the inner metal conductor 2 has a tapered structure and is connected to the RF connector 4, while the other end is connected to the DC blocking capacitor 1. The outer metal conductor 3 has a cylindrical hollow structure to enclose the inner metal conductor 2. The metal housing 5 is used to fix the inner metal conductor 2, the outer metal conductor 3, and the RF connector 4.

[0049] To achieve the above embodiments, the present invention also proposes a method for manufacturing a broadband high-voltage DC blocker suitable for power electronic equipment, including the use of high-conductivity materials for all metal structures, wherein the metal shell material can be stainless steel, conductive anodized aluminum alloy, or surface-protected pure copper, and the inner and outer conductor materials of the coaxial cable are pure copper with surface gold plating.

Claims

1. A design method for a broadband high-voltage DC blocker suitable for testing environments of power electronic equipment, characterized in that, Includes the following steps: Step 1: Based on the relationship between the characteristic impedance of the coaxial cable and the radii of its inner and outer conductors, and considering the breakdown voltage of the dielectric between the conductors, design a coaxial transmission line structure suitable for high-voltage environments. Step 2: Based on the measurement frequency range of the power electronic equipment, design the withstand voltage and capacitance value of the DC blocking capacitor so that the S-parameters of the DC blocking capacitor meet the performance requirements. Step 3: Design the interface adapter according to the requirements.

2. The design method as described in claim 1, characterized in that, Step 1 includes: calculating the inner and outer conductor radii of the coaxial cable based on the following two design requirements, optimizing the parameters using the Smith chart, and finally obtaining a coaxial transmission line structure suitable for high voltage: Requirement 1: Under the condition of achieving 50Ω impedance matching in a coaxial cable, the relationship between the characteristic impedance of the coaxial cable and the radii of its inner and outer conductors is expressed as follows: Among them, Z C The characteristic impedance of the coaxial cable is represented by r1, the inner conductor radius of the coaxial cable is represented by r2, the outer conductor radius of the coaxial cable is represented by σ1, the conductor conductivity of the coaxial cable is represented by d, the penetration depth of the conductor of the coaxial cable is represented by μ, the conductor permeability of the coaxial cable is represented by μ, the dielectric constant of the intermediate medium of the coaxial cable is represented by σ2, and the dielectric constant of the intermediate medium of the coaxial cable is represented by ε. Requirement 2: To ensure the coaxial cable can be used in high-voltage environments, the operating voltage of the power electronic equipment should be less than the breakdown voltage of the dielectric material between the conductors. When the dielectric material between the conductors is air, the relationship between the inner and outer conductor radii of the coaxial cable and the operating voltage of the power electronic equipment is as follows: Where d1 represents the distance between the two conductors in mm, p represents the gas pressure in atm, and f s V represents the safety factor. bias This indicates the DC bias voltage for the operation of power electronic equipment, expressed in kV.

3. The design method as described in claim 2, characterized in that, Step 102 includes the following: since the coaxial cable does not affect the S-parameter of the DC blocker under the condition of satisfying 50Ω impedance matching, the S-parameter of the DC blocker depends on the DC blocking capacitance. According to the normalized impedance of the DC blocking capacitor, The corresponding S-parameter matrix S is represented as follows: For the normalized impedance, S Blk Here are the S-parameters of the two-port network corresponding to the DC blocking capacitor, where j is the unit imaginary number, ω is the angular frequency, and C is the capacitance of the DC blocking capacitor. To ensure that the measurement signals from power electronic equipment can pass completely through the DC blocker and that low-frequency signals are sufficiently attenuated, the aforementioned S-parameter matrix must satisfy the following conditions based on the required measurement frequency range: 12 The cutoff frequency of the curve is less than 150kHz, and the frequency S is below 50Hz. 12 Less than -40dB, which means the following: S 12 (dB)| f＝50Hz ≈20lg(2πC·10 6 )<-40dB Among them, f C S represents 12 The cutoff frequency of the curve, S 12 (dB)| f＝50Hz S represents 12 The curve shows the decibel value at a frequency f equal to 50Hz. The estimated value of the DC blocking capacitor is obtained by solving: 9nF < C < 318nF nF is an international unit representing the capacitance. At the same time, the withstand voltage of the DC blocking capacitor should be greater than the DC bias voltage of the power electronic equipment to ensure that the DC blocking capacitor can be used in the high voltage and high current environment of the equipment.

4. A broadband high-voltage DC blocker suitable for power electronic equipment testing environments, characterized in that, It is obtained by the design method of any one of claims 1 to 3, and includes a DC blocking capacitor (1), a coaxial cable, an RF connector (4), and a metal shell (5). The coaxial cable includes a metal inner conductor (2) and a metal outer conductor (3). One end of the metal inner conductor (2) is connected to the RF connector (4) with a gradient structure, and the other end is connected to the DC blocking capacitor (1). The metal outer conductor (3) adopts a cylindrical hollow structure to surround the metal inner conductor (2). The metal shell (5) is used to fix the metal inner conductor (2), the metal outer conductor (3), and the RF connector (4).

5. The broadband high-voltage DC blocker suitable for power electronic equipment testing environments as described in claim 4, characterized in that, The metal casing material is stainless steel, conductive anodized aluminum alloy, or surface-protected pure copper.

6. The broadband high-voltage DC blocker suitable for power electronic equipment testing environments as described in claim 4, characterized in that, The inner and outer conductors of the coaxial cable are made of pure copper with a gold-plated surface.

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