Teaching Experiment Apparatus and Design Method for Conducted Electromagnetic Interference Measurement and Filtering Test of Power Supply Equipment

Abstract

This invention discloses a teaching experimental device for measuring and filtering conducted electromagnetic interference (EMI) in power supply equipment, including a conducted EMI experimental platform. The platform comprises a conducted EMI experimental module, a conducted EMI measurement module, and a computer, connected sequentially. This invention also discloses a design method for the teaching experimental device for measuring and filtering conducted EMI in power supply equipment. The experimental device designed by this invention can demonstrate the impact of changes in power supply operating conditions and circumstances on conducted EMI emission, while simultaneously solving the crosstalk problem between cables.

Description

Technical Field

[0001] This invention belongs to the technical field of practical teaching device development for electrical engineering majors in colleges and universities. It relates to a teaching experimental device for measuring and filtering conducted electromagnetic interference of power supply equipment. This invention also relates to the design method of the teaching experimental device for measuring and filtering conducted electromagnetic interference of power supply equipment. Background Technology

[0002] Currently, there is a lack of systematic teaching demonstrations for the standardized measurement of conducted electromagnetic interference (EMI), and there are no intuitive teaching demonstration devices for EMI filter design. Existing mature filtering devices are designed for single types of filters, such as passive EMI filters, active EMI filters, and digital active EMI filters. However, for power supplies with wide bandwidth and complex electromagnetic environments, hybrid EMI filters that combine the advantages of various filters are more suitable for the needs of power supplies. However, there is currently no device that can intuitively demonstrate the difference in filtering capabilities between hybrid and single filters under different power supplies. Furthermore, during conducted EMI measurement, the placement of the power supply equipment and the layout of connecting cables can affect conducted EMI, leading to low measurement accuracy and inaccurate prediction of filtering performance. Summary of the Invention

[0003] The purpose of this invention is to provide a teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment. This device enables switching between single filtering and hybrid filtering in the teaching device, while also solving the problem of crosstalk between cables.

[0004] Another objective of this invention is to provide a design method for a teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment.

[0005] The first technical solution adopted in this invention is a teaching experimental device for measuring and filtering conducted electromagnetic interference of power supply equipment, including a conducted EMI experimental platform, on which a conducted EMI experimental module, a conducted EMI measurement module, and a computer are connected in sequence.

[0006] The first technical solution of this invention is further characterized by:

[0007] The conducted EMI test module consists of a measurement board, a filtering board, and a power load board connected in sequence.

[0008] The measurement module includes two impedance stabilizers. The L and N AC power lines are connected to the two impedance stabilizers respectively. The PE line is first connected to the PE switching module and then to the two impedance stabilizers. One end of each impedance stabilizer is connected to one end of the filter mode switching module, and the other end of the filter mode switching module is the OUT output terminal.

[0009] The filtering module includes a filter module, and the input and output ends of the filter module are connected to a slide groove. Each slide groove is provided with three wire clamps at equal intervals.

[0010] The power load section includes a test subject module. The positive and negative lines of the DC power supply in the test subject module are connected to the load module. One end of the test subject module is connected to the controller. The other end of the controller is connected to the duty cycle regulator and the switching frequency regulator, respectively. A wire clamp is installed between the test subject module and the controller to fix the signal line. The wire clamp is installed on the slide.

[0011] The load module includes n load resistors and n load switching switches, with each load resistor connected in series with one load switching switch.

[0012] The filter module includes parallel L1, N1, and PE1 lines. A passive filter module is connected in series on the L1, N1, and PE1 lines. An active filter module and a digital active filter module are also connected in parallel on the L1, N1, and PE1 lines. The passive filter module has a filter mode switching switch at each end. The active filter module and the digital active filter module each have a filter mode switching switch on the connection lines to the L1, N1, and PE1 lines.

[0013] The second technical solution adopted in this invention is a design method for a teaching experimental device for measuring and filtering conducted electromagnetic interference of power supply equipment, including the design of the distance l1 between the conducted EMI experimental platform, the impedance stabilizer and the test object module, and the spacing of the wire clamp.

[0014] The second technical solution of the present invention is further characterized by:

[0015] The design process for the platform height h of the conducted EMI test platform is as follows:

[0016] Based on the capacitive coupling mechanism of power supply devices, the power supply device generates a parasitic capacitance C through the switching transistor and the metal base plate. k The height h of the EMI experimental platform and the parasitic capacitance C k The relevant formula is:

[0017]

[0018] Where ε0 is the vacuum permittivity; ε r1 a is the relative permittivity; SMPS For the length of the power supply equipment; b SMPS The width of the power supply equipment; based on the common-mode noise loop formed by the power supply equipment and the impedance stabilizer, the common-mode noise loop satisfies the following equation:

[0019]

[0020] Among them, U CM For common-mode interference source voltage; I EMI For common-mode interference current; R LISN C is the internal resistance of the impedance stabilizer. LISN C is the internal capacitor of the impedance stabilizer; k f is the parasitic capacitance between the switching transistor and the metal base plate. SMPS This is the switching frequency of the switching transistor;

[0021] The platform height h of the conducted EMI test platform satisfies the following relationship:

[0022]

[0023] The distance from the conducted EMI experimental module to the rear metal side plate is x. Based on the capacitive coupling mechanism of the power supply equipment, a common-mode noise circuit is constructed. According to formulas (1) to (3), the magnitude of x satisfies:

[0024]

[0025] Where x0 is the distance between the power supply device and the wall;

[0026] The design process for the distance l1 between the impedance stabilizer and the test subject module is as follows:

[0027] Based on the principle of conducted coupling, the PE line is shared in the common-mode circuits of both the L line and the N line. When there is interference current in the L line, the interference voltage generated on the L line will affect the N line, resulting in conducted coupling. The following formula is obtained from the equivalent circuit of conducted coupling in the L line common-mode loop:

[0028]

[0029] Where, k c For crosstalk between the L line and the PE line; U CM Z is the common-mode interference source voltage; L1 Z is the load impedance between the L line and the PE line; L2 Z is the load impedance between the N line and the PE line; S1 Z is the source impedance between the L line and the PE line; S2 Z is the source impedance between the N-line and the PE-line; C The impedance of the PE line;

[0030] PE line impedance Z C The impedance Z is related to the distance l1 between the impedance stabilizer and the subject module. C Expressed using formula (6):

[0031]

[0032] Where, ρ lineThe resistivity of the conductor;

[0033] According to formulas (5) and (6), the distance l1 between the impedance stabilizer and the subject module is:

[0034]

[0035] Where, k c For crosstalk between the L line and the PE line; Z L1 Z is the load impedance between the L line and the PE line. L2 Z is the load impedance between the N line and the PE line. S2 ρ is the source impedance between the N-line and the PE-line. line ρ is the resistivity of the conductor.

[0036] The design process for the spacing of the wire clamp is as follows:

[0037] The input and output terminals of the filter module are each connected to a set of sliding grooves. Three wire clamps are equidistantly arranged within each set of sliding grooves. The two sets of sliding grooves and their corresponding three wire clamps constitute H1 and H2. H1 is located between the impedance stabilizer and the filter module; H2 is located between the filter module and the test subject module. The distance d1 between the L-line and the N-line is adjusted by moving the wire clamps on the sliding grooves. The design process for the distance d1 between the L-line and the N-line is as follows:

[0038] Based on the electric field coupling theory, when common-mode noise voltage is present, the L-line and N-line will generate a coupling capacitance C when they are close to each other. LN This leads to crosstalk between the L line and the N line. Based on the equivalent circuit of the capacitive coupling between the L line and the N line, the following formula (8) is obtained:

[0039]

[0040] Where, k t For crosstalk between L line and N line; Z L1 Z is the load impedance between the L line and the PE line; L2 Z is the load impedance between the N line and the PE line; S1 Z is the source impedance between the L line and the PE line; S2 The source impedance between the N-line and the PE-line; C LG The capacitance between line L and ground; C NG The capacitance between the neutral (N) line and ground; C LN f is the coupling capacitance between the L line and the N line; SMPS This is the switching frequency of the switching transistor;

[0041] According to the principle of interconductor capacitance, the L-line and N-line generate a coupling capacitance at high frequencies. This coupling capacitance C LN The capacitance C is related to the spacing d1 between the two lines. LNExpressed using formula (9):

[0042]

[0043] Where ε0 is the dielectric constant of air; d1 is the distance between the L-line and N-line; l1 is the distance between the impedance stabilizer and the test subject module; r line Let be the radius of the conductor;

[0044] According to the principle of a parallel-plate capacitor, the L-line and N-line generate a capacitance C to ground at high frequencies. LG and an N-line to ground capacitance C NG These two capacitors are related to the height h of the conducted EMI test platform, and the capacitance C LG and C NG Expressed using formula (10):

[0045]

[0046] Where l1 is the distance between the impedance stabilizer and the subject module; r line Let be the radius of the conductor;

[0047] According to formulas (8) to (10), the distance d1 between line L and line N is:

[0048] d1 = 2r line e m (11)

[0049] in:

[0050]

[0051] k t Z represents the crosstalk between the L-line and the N-line, where ε0 is the relative permittivity; L1 Z is the load impedance between the L line and the PE line. S1 f is the source impedance between the L line and the PE line. SMPS The switching frequency of the switching transistor; to balance the common-mode interference between the L and N lines, the distances from the PE line to the L line and from the PE line to the N line are:

[0052] A wire clamp is installed between the test subject module and the controller to fix the signal line. The wire clamp is installed on the slide groove to form H3. The distance d2 between the controller's signal line and the power supply line is adjusted by moving the wire clamp on the slide groove. Based on the electric field coupling theory, according to formulas (8) to (12), the distance d2 between the controller's signal line and the power supply line satisfies the following relationship:

[0053] d2=2r line e n (13)

[0054] in:

[0055]

[0056] The beneficial effects of this invention are as follows: The teaching experimental device for measuring and filtering conducted electromagnetic interference (EMI) in power supply equipment proposed in this invention considers the generation mechanism of conducted EMI and the influencing factors of conducted EMI in power supply equipment, and designs a teaching device that can demonstrate the transmission process of EMI in power supply equipment as the test conditions change. In the design method of this invention, starting from the suppression capability of the filter on the filtered system, the impedance mismatch effect between the filter and the source impedance and load impedance is considered. By designing the filter module in the device, the filtering performance of passive, active, digital active, and hybrid filters on the filtered object can be tested. The design method of this invention also considers the crosstalk problem between cables, which can quantitatively obtain the cable layout parameters, thereby improving measurement accuracy. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the structure of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment according to the present invention;

[0058] Figure 2 This is a structural diagram of the conducted EMI experimental module of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment according to the present invention;

[0059] Figure 3 This is a structural diagram of the filter module of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment according to the present invention;

[0060] Figure 4 This is a waveform diagram of conducted EMI emission measurement of the teaching experimental device for conducting electromagnetic interference measurement and filtering test of power supply equipment according to the present invention;

[0061] Figure 5 The passive filtering mode performance test waveform diagram of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power equipment according to the present invention is shown.

[0062] Figure 6 The waveform diagram for the active filter mode performance test of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power equipment according to the present invention is shown.

[0063] Figure 7 The waveform diagrams are for the passive and active filtering hybrid mode performance test of the teaching experimental device for measuring and filtering conducted electromagnetic interference of power equipment according to the present invention.

[0064] In the diagram, 1. Conducted EMI experimental module, 2. Conducted EMI measurement module, 3. Computer, 4. Conducted EMI experimental platform, 5. Impedance stabilizer, 6. Filter module, 7. Subject module, 8. Load module, 9. Controller, 10. Filter mode switching module, 11. Load resistor, 12. CM / DM calculation module, 13. Slide rail, 14. Wire clamp, 15. PE continuity module, 16. Load switching switch, 17. Filter mode switching switch, 18. Duty cycle adjuster. 9. Switching frequency regulator; 20. Passive filter module; 21. Active filter module; 22. Digital active filter module; 23. Filter module switching switch; 24. Passive filter device switching switch; 25. Filter inductor; 26. Filter capacitor; 27. Detection network; 28. Operational network; 29. ​​Injection network; 30. ADC module; 31. FPGA module; 32. DAC module; 33. Amplification network; 34. Measurement board; 35. Filtering board; 36. Power supply load board. Detailed Implementation

[0065] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0066] Example 1

[0067] This invention relates to a teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment, such as... Figure 1 As shown, the system includes a conducted EMI experimental module 1, a conducted EMI (Electromagnetic Interference) measurement module 2, a computer 3, and a conducted EMI experimental platform 4. The conducted EMI experimental module 1 consists of three main sections: a measurement module 34, a filtering module 35, and a power supply load module 36. The conducted EMI measurement module 2 uses Rohde & Schwarz... It can measure the conducted EMI spectrum of the switching power supply. Computer 3 uses a Lenovo Ideapad 330 with a Win10 operating system and EMI spectrum measurement host computer software, which can display and control the EMI spectrum measured by conducted EMI measurement module 2. The measurement board 34 in conducted EMI experimental module 1 and conducted EMI measurement module 2 are connected by an RF cable, and conducted EMI measurement module 2 and computer 3 communicate via Ethernet. Conducted EMI experimental module 1, conducted EMI measurement module 2 and computer 3 are located on the platform of conducted EMI experimental platform 4.

[0068] The structural diagram of the conducted EMI experimental module of the teaching experimental device for conducting electromagnetic interference measurement and filtering of power supply equipment of this invention is shown in the figure below. Figure 2 As shown, it includes three modules: measurement module 34, filtering module 35, and power load module 36.

[0069] Example 2

[0070] The measurement module 34 includes an impedance stabilizer 5, a filter mode switching module 10, and a PE switching module 15. The connections are as follows: the L and N AC power lines are connected to the two impedance stabilizers 5 respectively; the PE line is first connected to the PE switching module 15 and then to the two impedance stabilizers 5, connecting them together. One end of the filter mode switching module 10 is connected to the two impedance stabilizers 5, and the other end is the OUT output terminal. Internally, the filter mode switching module 10 consists of a CM / DM calculation module 12 and a filter mode switching switch 17. The PE (Protective Earthing) switching module 15 can switch the conducted EMI experimental module 1 between grounded and ungrounded modes, facilitating students' understanding and analysis of the conducted EMI flow path of the system with and without a ground wire. The impedance stabilizer 5 can provide a stable 50Ω load impedance. The CM / DM (Common Mode / Differential Mode) calculation module 12 can calculate the conducted EMI on the L and N lines, thus obtaining the CM and DM noise on the line. The filter mode switch 17 allows you to select the type of conducted EMI to be measured.

[0071] Example 3

[0072] The filter module 35 includes a filter module 6, a slide rail 13, and wire clamps 14. The connections between the modules are as follows: the input and output terminals of the filter module 6 are connected to one slide rail 13 and three wire clamps 14; each wire clamp 14 secures one line on the input or output terminal of the filter module 6, and the three wire clamps 14 on each side are mounted on one slide rail 13, forming two groups, H1 and H2. The slide rail 13 and wire clamps 14 secure the connecting lines between the modules and control the distance between these connecting lines, thereby reducing interference between the L and N lines.

[0073] Example 4

[0074] The power load module 36 includes a test module 7, a load module 8, a controller 9, a slide rail 13, a wire clamp 14, a duty cycle regulator 18, and a switching frequency regulator 19. The connections between the modules are as follows: the positive and negative wires of the DC power supply line from the test module 7 are connected to the load module 8; one end of the controller 9 is connected to the test module 7, and the other end is connected to the duty cycle regulator 18 and the switching frequency regulator 19. A wire clamp 14 is installed between the test module 7 and the controller 9 to secure the signal line; the wire clamp 14 is mounted on the slide rail 13, forming a set H3. The load module 8 includes resistors R1, R2 to R... nThere are n load resistors 11 and n load switching switches 16, K1, K2 to Kn, with each load resistor 11 connected in series with one load switching switch 16. The corresponding load is connected by pressing different load switching switches 16. The PWM output of the controller 9 is changed by rotating the knobs of the duty cycle adjuster 18 and the switching frequency adjuster 19, thereby changing the operation of the switching transistor in the test module 7 and controlling the test module and the entire EMI test module. The slide 13 and the wire clamp 14 fix the signal line between the test module 7 and the controller 9 and control the distance between the signal line and the DC power line, thereby reducing interference between the power line and the signal line.

[0075] The impedance stabilizer 5 in the measurement plate 34 is connected to H1, which consists of a slide 13 and three wire clamps 14 in the filter plate 35; the test subject module 7 in the power load plate 36 is connected to H2, which consists of a slide 13 and three wire clamps 14 in the filter plate 35.

[0076] Example 5

[0077] The structural diagram of filter module 6 of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment of the present invention is shown in the figure below. Figure 3As shown, the system includes a passive filter module 20, an active filter module 21, a digital active filter module 22, a filter mode switch 23, and three power lines: L1, N1, and PE1. A passive filter module 20 is connected in series on the L1, N1, and PE1 lines of filter module 6. The active filter module 21 and the digital active filter module 22 are connected in parallel on the L1, N1, and PE1 lines. At each end of the passive filter module 20, there is a filter mode switch 23, designated T2 and T3. A branch of the filter mode switch 23, designated T1, is connected in parallel outside these two filters. On the connection lines between the active filter module 21 and the digital active filter module 22 and the L1, N1, and PE1 lines, there are filter mode switches 23, designated T4, T5, T6, and T7, respectively. Students can connect different filters to the filtered system by switching different filter mode switches 23, thus testing the filtering performance of a single filter or the filtering performance of a mixture of passive and active, digital and analog filters. Furthermore, switching the filter mode switches 23 allows for easy connection and disconnection of filters in the filtered system, facilitating the calculation of insertion loss IL. The passive filter module 20 includes passive filter structure switching switches 24, filter inductors 25, and filter capacitors 26. There are 12 passive filter structure switching switches 24, numbered S1, S2 to S12; 6 filter inductors 25, all connected in series between lines L1 and N1, denoted by L; and 6 filter capacitors 26, with two connected in parallel between lines L1 and N1, denoted by C. x This indicates that there are four lines connected in parallel between L1 or N1 and PE1, represented by C. y Students can connect different filter inductors 25 and filter capacitors 26 to the circuit by turning different passive filter structure switching switches 24 on and off, thereby forming common-mode or differential-mode passive EMI filters of different structure types, such as C-type, L-type, Γ-type, inverse Γ-type, T-type and Π-type.

[0078] The active filter module 21 includes a detection network 27, a computation network 28, and an injection network 29.

[0079] The digital active filter module 22 includes a detection network 27, an injection network 29, an ADC (Analog-to-Digital Converter) module 30, an FPGA (Field-Programmable Gate Array) module 31, a DAC (Digital-to-Analog Converter) module 32, and an amplification network 33. This filter module serves as a conducted EMI suppressor for students completing experiments on conducted electromagnetic interference suppression in switching power supplies. It incorporates emerging technologies in conducted EMI filtering, allowing students to learn about filter suppression principles and selection while mastering the knowledge points of active EMI filters, digital active EMI filters, and hybrid filter suppression. It enables students to intuitively understand the impact of different filters on filtering performance, as well as the changes in filtering performance caused by hybrid filters.

[0080] The conducted EMI emission measurement waveform of the teaching experimental device for conducting electromagnetic interference measurement and filtering of power supply equipment of this invention is shown in the figure below. Figure 4 As shown (without a filtered power supply), this waveform represents the conducted EMI emission measured on the L-line of a test subject in unfiltered mode with a 50% duty cycle, a switching frequency of 150kHz, and a load resistance of 50Ω. Switches K3 (n=3 in load switching switch 16) and T1 are closed, all other switches are open, and the filter mode switch is set to the L-line of the switching power supply. This waveform is in the frequency domain, ranging from 150kHz to 30MHz, with amplitudes from 23dBμV to 67dBμV. Twenty frequency points exceed the specified horizontal line on the waveform, with the largest exceeding the limit by 12dB.

[0081] The passive filtering mode performance test waveform of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment of this invention is shown in the figure below. Figure 5 As shown, this waveform represents the conducted EMI emission measured on the L-line of a test subject with a 50% duty cycle, a switching frequency of 150kHz, and a load resistance of 50Ω, in passive filtering mode using an L-line-common-mode-T-type passive EMI filter. Switches K3 (n=3 in load switching switch 16), T2, T3, S3, S4, S5, S6, and S9 are closed, while the remaining switches are open. The filter mode switch is set to the L-line of the switching power supply. This waveform is in the frequency domain, with frequencies ranging from 150 to 30MHz and amplitudes from 20dBμV to 57dBμV. All frequencies on the waveform are below the specified horizontal line, with differences between them ranging from 10 to 20dB.

[0082] The waveform diagram of the active filter mode performance test of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment of this invention is shown below. Figure 6 As shown, this waveform represents the conducted EMI emission measurement waveform on the L-line of a test subject in active filtering mode with a duty cycle of 50%, a switching frequency of 150kHz, and a load resistance of 50Ω. Switches K3 (n=3 in load switching switch 16), T1, T4, and T5 are closed, while the remaining switches are open. The filter mode switch is set to the L-line of the switching power supply. This waveform is a frequency domain waveform, with frequencies ranging from 150kHz to 30MHz and amplitudes from 20dBμV to 37dBμV. All frequencies on the waveform are below the specified horizontal line, with differences between them ranging from 20 to 25dB.

[0083] The waveform diagram of the passive and active filtering hybrid mode performance test of the teaching experimental device for conducting electromagnetic interference measurement and filtering of power supply equipment of this invention is shown in the figure. Figure 7 As shown, this waveform represents the measured conducted EMI emission waveform on the L-line of the test subject under a 50% duty cycle, 150kHz switching frequency, and 50Ω load resistance in a mixed passive and active filtering mode. The passive filter used is an L-line common-mode T-type passive EMI filter. Switches K3 (n=3 in load switching switch 16), T2, T3, T4, T5, S3, S4, S5, S6, and S9 are closed, while the remaining switches are open. The filter mode switch is set to the L-line of the switching power supply. This waveform is a frequency domain waveform, with frequencies ranging from 150kHz to 30MHz and amplitudes from 20dBμV to 33dBμV. All frequencies on the waveform are below the specified horizontal line, with differences between them ranging from 25 to 30dB.

[0084] Example 6

[0085] The design method of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment according to the present invention is as follows:

[0086] (1) Design of Conducted EMI Experiment Platform 4: The bottom surface of the conducted EMI experiment platform 4 is a metal base plate, the rear side is a metal side plate, and the rest is made of non-conductive wood material. These two metal plates are connected to the ground. To ensure that sufficiently large conducted electromagnetic interference can be measured in experimental teaching, and considering the working environment of the power supply equipment, the design of the platform height h of the entire conducted EMI experiment platform 4 is as follows: Based on the capacitive coupling mechanism of the power supply equipment, the power supply equipment generates a parasitic capacitance C through the switching transistor and the metal base plate. k The platform height h and the parasitic capacitance C k The relevant formula is as follows:

[0087]

[0088] Where ε0 is the vacuum permittivity; ε r1Let a be the relative permittivity of the wooden platform between the power supply equipment and the metal base (its permittivity is taken as 4); SMPS For the length of the power supply equipment; b SMPS The common-mode electromagnetic interference (EME) of a power supply device is limited; it only exists if a common-mode noise loop is present. Based on the common-mode noise loop formed by the power supply device and the impedance stabilizer, the KVL equation for this loop is:

[0089]

[0090] Among them, U CM For common-mode interference source voltage; I EMI For common-mode interference current; R LISN C is the internal resistance of the impedance stabilizer. LISN C is the internal capacitor of the impedance stabilizer; k f is the parasitic capacitance between the switching transistor and the metal base plate. SMPS Let h be the switching frequency of the switching transistor. From formula (1), it can be seen that the larger the platform height h is, the greater the parasitic capacitance C generated between the switching transistor and the metal base plate. k The smaller the value, the better. From formula (2), we can see that the parasitic capacitance C generated by the switching transistor and the metal base plate... k The smaller the common-mode interference current I, the lower the common-mode interference current I. EMI The smaller the value. Electromagnetic interference noise is measured by the voltage across the internal resistor of the impedance stabilizer, which is related to the common-mode interference current I. EMI Regarding this, to prevent the electromagnetic interference noise voltage measured by students from being too low and thus unsuitable for teaching demonstrations, it is stipulated that the minimum noise voltage should not be lower than one-tenth of the common-mode interference source voltage. Simultaneously, to simulate the working scenario of power supply equipment, the platform height should not be lower than the ground clearance of commonly used power supply equipment. Based on this, the platform height h of the conducted EMI experimental platform 4 can be derived as follows:

[0091]

[0092] Where h0 is the ground clearance of commonly used power supply equipment, and h0 is taken as 0.8m for equipment below 500W; ε0 is the vacuum permittivity; ε r1 Let a be the relative permittivity of the wooden platform between the power supply equipment and the metal base (its permittivity is taken as 4); SMPS For the length of the power supply equipment; b SMPS For the width of the power supply equipment; R LISN C is the internal resistance of the impedance stabilizer. LISN f is the internal capacitor of the impedance stabilizer; SMPSLet x be the switching frequency of the switching transistor. The distance from the conducted EMI experimental module 1 to the rear metal side plate is x. In order to ensure that sufficiently large conducted electromagnetic interference can be measured in the experimental teaching, and to prevent the conducted electromagnetic interference from being too large and causing damage to the power supply equipment, a common-mode noise circuit is constructed based on the capacitive coupling mechanism of the power supply equipment. According to formulas (1) to (3), the magnitude of x should satisfy:

[0093]

[0094] Where x0 is the distance between commonly used power supply equipment and the wall, typically taken as 0.1m; ε0 is the vacuum permittivity; ε r2 Let be the relative permittivity of the air between the power supply equipment and the metal side plate (its permittivity is taken as 1.00053); a SMPS For the length of the power supply equipment; c SMPS For high power supply equipment; R LISN C is the internal resistance of the impedance stabilizer. LISN f is the internal capacitor of the impedance stabilizer; SMPS denoted as the switching frequency of the switching transistor. When simulating a desktop power supply, the platform height h of the conducted EMI test platform 4 is designed according to formula (3), and the distance x from the conducted EMI test module 1 to the rear metal side plate is 0.1m; when simulating a wall-mounted power supply, the platform height h of the conducted EMI test platform 4 is 0.8m, and the distance x from the conducted EMI test module 1 to the rear metal side plate is designed according to formula (4).

[0095] (2) Design of impedance stabilizer 5: When performing filter performance testing, in order to facilitate the consideration of the impedance matching problem of the load impedance, a stable 50Ω load impedance needs to be provided at the input end. Therefore, the Rohde & Schwarz V-NETWORK·ESH3-Z6 is selected.

[0096] (3) Design of Subject Module 7: For Subject Module 7, this invention targets conducted electromagnetic interference of switching power supplies; therefore, Subject Module 7 is a switching power supply module with controllable switching transistors. This switching power supply module is designed as a combination of AC / DC and DC / DC switching power supplies. The AC / DC converter uses a bridge fully controlled rectifier circuit, and the DC / DC converter uses a flyback circuit. The input voltage of the switching power supply is 220VAC, the output voltage is adjustable from 5-48V DC, and the switching frequency of the switching transistor is adjustable from 50kHz to 200kHz. For the driving circuit of the switching transistor, Infineon's 1ED020I12-F2 driver chip is used to drive the switching transistor.

[0097] (4) Design of the distance l1 between impedance stabilizer 5 and test subject module 7: In this invention, in order to improve the accuracy of the conducted electromagnetic interference measured by the test subject, facilitate students' understanding of the conducted electromagnetic interference characteristics of the L line and N line, and reduce the influence of crosstalk between the L line and N line on the test results, it is necessary to design the distance l1 between impedance stabilizer 5 and test subject module 7: Based on the theory of conducted coupling, the PE line is shared in the common mode circuit of the L line and N line. When there is interference current in the L line, the interference voltage generated on the L line will affect the N line, resulting in conducted coupling. According to the equivalent circuit of conducted coupling in the common mode circuit of the L line, we can obtain:

[0098]

[0099] Where, k c For crosstalk between the L line and the PE line; U CM Z is the common-mode interference source voltage; L1 Z is the load impedance between the L line and the PE line; L2 Z is the load impedance between the N line and the PE line; S1 Z is the source impedance between the L line and the PE line; S2 Z is the source impedance between the N-line and the PE-line; C This refers to the PE line impedance. The PE line impedance Z... C The impedance Z is related to the distance l1 between the impedance stabilizer 5 and the subject module 7. C It can be expressed by formula (6), where ρ line The resistivity of the conductor;

[0100] Z C =ρ line l1 (6)

[0101] According to formulas (5) and (6), the distance l1 between the impedance stabilizer 5 and the subject module 7 can be obtained as:

[0102]

[0103] Where, k c To account for crosstalk between the L line and the PE line, set the value to 0; Z L1 The load impedance between the L line and the PE line is 50Ω, provided by the impedance stabilizer; Z L2 The load impedance between the N and PE lines is 50Ω, provided by the impedance stabilizer; Z S2 The source impedance between the N-line and the PE-line is taken as 50Ω; ρ line ρ is the resistivity of the conductor.

[0104] (5) Design of controller 9: In order to control the test subject module 7 in real time, the duty cycle and switching frequency of the switching transistor can be adjusted. Texas Instruments' TMS320F28335 real-time microcontroller is selected.

[0105] (6) Design of Duty Cycle Regulator 18 and Switching Frequency Regulator 19: The design parameters of the duty cycle regulator 18 and the switching frequency regulator 19 are exactly the same, and the selected models are also exactly the same. In order to facilitate students to intuitively adjust the duty cycle and switching frequency of the switching transistor of the test subject module, a potentiometer of model 3590S-2-103L is selected. The accuracy of this potentiometer is ±5%, and the rated power is 2W.

[0106] (7) Design of Load Module 8: Load module 8 has n load resistors 11 and n load switching switches 16. Based on the output voltage of the switching power supply and the different load resistors, different power levels of the load P0 can be simulated. Students can connect different loads by pressing different load switching switches 16 according to the required load power level. This invention will use 3 load resistors and 3 load switching switches as an example to describe the switching strategy for power supply device power realization. The load resistors are R1 = 10Ω, R2 = 20Ω and R3 = 50Ω, and the rated output voltage U0 of the switching power supply is 48V.

[0107] The maximum rated power P of the load resistor is calculated based on the rated output voltage U0 of the test subject. emax for: Where R1||R2 represents the minimum load resistance under this switching strategy example. Since 345.43W < 400W, the load resistor selected in this invention has a power rating of 400W. The selected load resistors are from Fenghua Advanced Technology Co., Ltd. A load switching switch 16 is connected in series in each branch of the load resistor, for a total of three switches. These three load switching switches have identical design parameters and are of the same model. Based on the maximum current and voltage on the output side, this invention selects a single-pole single-throw toggle switch M2011B2B1W02, with a rated voltage of 125V and a rated current of 4A.

[0108] The switching strategy for power supply device power implementation is as follows:

[0109] When simulating power devices such as chargers with a power of less than 100W, the load power P0 satisfies At this point, switch K3 should be closed, and switches K1 and K2 should be opened.

[0110] When simulating power supplies with a power consumption of 100-150W, such as laptops, the load power P0 satisfies... At this point, switch K2 should be closed, and switches K1 and K3 should be opened.

[0111] When the power supply device, such as an analog television, has a power of 150-200W, the load power P0 satisfies... At this point, switches K2 and K3 should be closed, and switch K1 should be turned on.

[0112] When simulating power devices with a power of 200-250W, such as a refrigerator, the load power P0 satisfies... At this point, switch K1 should be closed, and switches K2 and K3 should be turned on.

[0113] When simulating power supply devices with a power of 250-300W, such as water dispensers, the load power P0 satisfies... At this point, switches K1 and K3 should be closed, and switch K2 should be turned on.

[0114] When simulating power devices with a power of 300-350W, such as a washing machine, the load power P0 satisfies... At this point, switches K1 and K2 should be closed, and switch K3 should be turned on.

[0115] For example, when U0 is 48V, to simulate the conducted electromagnetic interference of an energy-saving lamp, considering that the power of the energy-saving lamp is below 100W, it must meet the following conditions: At this point, switch K3 is closed, and switches K1 and K2 are turned on. The switching strategy is similar when simulating power devices of other power levels.

[0116] This invention uses three load resistors as an example to simulate conducted electromagnetic interference in power supply devices with a power rating of less than 350W. To increase the power rating of the power supply device or to further subdivide the power rating of the power supply device, the number of load resistors can be increased and load resistors with different resistance values ​​can be selected.

[0117] (8) Design of PE continuity module 15: The PE continuity module 15 of this invention, through the connection and disconnection interface, transforms the entire conducted EMI measurement module 2 into two states: with PE ground and without PE ground. The PE continuity module 15 is connected using a banana plug connector. Since it is installed at the input end of the conducted EMI measurement module 2, an ams 25.502.1 banana plug is selected. The product has a rated voltage of 600V and a rated current of 32A.

[0118] (9) Design of the spacing of the wire clamps 14: This invention has three sets of slides and wire clamps, of which H1 and H2 consist of one slide and three wire clamps, located between the impedance stabilizer 5 and the filter module 6 and between the filter module 6 and the test subject module 7. The distance d1 between the L line and the N line can be adjusted by moving the wire clamps on the slide. The design of the distance d1 between the L line and the N line is as follows: Based on the electric field coupling theory, when the common-mode noise voltage exists, the L line and the N line will generate a coupling capacitance C when they approach each other. LNThis leads to crosstalk between the L line and the N line. Based on the equivalent circuit of the capacitive coupling between the L line and the N line, we can obtain:

[0119]

[0120] Where, k t For crosstalk between L line and N line; Z L1 Z is the load impedance between the L line and the PE line; L2 Z is the load impedance between the N line and the PE line; S1 Z is the source impedance between the L line and the PE line; S2 The source impedance between the N-line and the PE-line; C LG The capacitance between line L and ground; C NG The capacitance between the neutral (N) line and ground; C LN f is the coupling capacitance between the L line and the N line; SMPS This represents the switching frequency of the switching transistor.

[0121] According to the principle of interconductor capacitance, the L-line and N-line will generate coupling capacitance at high frequencies (above 20kHz). This coupling capacitance C LN The capacitance C is related to the spacing d1 between the two lines. LN It can be expressed by formula (9).

[0122]

[0123] Where ε0 is the dielectric constant of air; d1 is the distance between the L-line and N-line; l1 is the distance between the impedance stabilizer and the test subject module; r line Let be the radius of the conductor.

[0124] According to the principle of a parallel-plate capacitor, the L-line and N-line will generate an L-line-to-ground capacitance C at high frequencies. LG and an N-line to ground capacitance C NG These two capacitors are related to the height h of the conducted EMI test platform. The capacitor C... LG and C NG It can be expressed by formula (10).

[0125]

[0126] Where ε0 is the relative permittivity; ε r1 ρ is the relative permittivity of the wooden platform between the power supply equipment and the metal base plate (its permittivity is taken as 4); h is the height of the conducted EMI test platform; l1 is the distance between the impedance stabilizer and the test module; r line Let be the radius of the conductor. According to formulas (8) to (10), the distance d1 between line L and line N can be obtained as:

[0127] d1 = 2rline e m (11)

[0128]

[0129] Where, k t The crosstalk between the L line and the N line is set to 0; ε0 is the relative permittivity; ε r1 Z represents the relative permittivity of the wooden platform between the power supply equipment and the metal base (its permittivity is taken as 4); L1 The load impedance between the L line and the PE line is 50Ω, provided by the impedance stabilizer; Z S1 The source impedance between the L-line and the PE-line is taken as 50Ω; f SMPS is the switching frequency of the switching transistor; h is the height of the conducted EMI test platform; l1 is the distance between the impedance stabilizer and the test module; r line Let be the radius of the conductor. To balance the common-mode interference between the L and N lines, the distances from the PE line to the L and N lines must be consistent, i.e., the distances from the PE line to the L line and the distances from the PE line to the N line are . H3 consists of a slide and a wire clamp, located between the test subject module 7 and the controller 9. The distance d2 between the controller's signal line and the power supply line can be adjusted by moving the wire clamp on the slide. Based on the electric field coupling theory, the design of the distance d2 between the controller's signal line and the power supply line can be obtained according to formulas (8) to (12):

[0130] d2=2r line e n (13)

[0131]

[0132] Where: k s The crosstalk between the power line and the signal line is set to 0; ε0 is the relative permittivity; ε r1 Z represents the relative permittivity of the wooden platform between the power supply equipment and the metal base (its permittivity is taken as 4); L Z represents the load impedance on the output side of the power supply line. Lx Z represents the load impedance of the signal line to ground, taken as 50Ω. S Z represents the source impedance of the power line to ground, taken as 50Ω. Sx The source impedance of the signal line to ground is taken as 50Ω; f SMPS l1 is the switching frequency of the switching transistor; h is the height of the conducted EMI test platform; l2 is the length of the power line conductor; l3 is the length of the signal line conductor; r line Let be the radius of the conductor. The distance d2 between the controller's signal line and the power supply line, and its relationship to the load impedance Z on the output side of the power supply line. LRelated to the load impedance Z L In this invention, the resistance value is consistent with that of the load resistor. Therefore, when different load resistors are selected to simulate power supply devices with different power, the distance d2 between the controller signal line and the power supply line will be adjusted according to formula (13).

[0133] (10) Design of Filtering Mode Switching Module 10: The filtering mode switching module 10 consists of a CM / DM calculation module 12 and a filtering mode switching switch 17. The CM / DM calculation module 12 uses a CYBERTEK EM5016A, which can process conducted EMI on the L and N lines, thus obtaining the CM and DM noise on the line. The filtering mode switching switch 17 uses a four-contact rotary switch MFR01-A2F03LIS-R, which can select the L line, N line, CM, and DM conducted EMI of the switching power supply. (This is related to...) Figure 3 The design process of filter module 6 is as follows:

[0134] (1) Design of the filter module switching switch 23: To achieve switching between different filters and to simultaneously turn on and off the L line, N line, and PE line, considering that the main line voltage is 220VAC, the filter module switching switch 23 adopts a three-pole single-throw toggle switch 651H / 2, with a rated voltage of 250VAC and a rated current of 15A. Students switch between different filters by toggling different filter mode switching switches 23, as shown in Table 1. It can switch to a single filter or a hybrid filter between passive and active, digital and analog. It can demonstrate the filtering performance of a single filter to students, as well as the hybrid filtering capability under complex working conditions. Furthermore, it is convenient to switch between the filter-without-filter mode and the filter-without-filter mode, facilitating students' measurement and calculation of insertion loss IL.

[0135] Table 1 Filter Mode Switching Table

[0136]

[0137]

[0138] (2) Design of Passive Filter Module 20: The passive filter module 20 includes 12 passive filter structure switching switches 24, 6 filter inductors 25, and 6 filter capacitors 26. The passive filter structure switching switches 24 are single-pole single-throw toggle switches 631H / 2, with a rated voltage of 250V and a rated current of 15A. The filter inductors 25 have a value of L = 5mH, and the filter capacitors 26 are divided into common-mode capacitors C... y Sum and difference mode capacitors C x The value is C y =1μF and C x=470nF. The selected filter inductor and capacitor are manufactured by Fenghua Advanced Technology. The passive filter module 20 takes into account the source impedance Z of the filtered system. S and load impedance Z L The relationship between them is achieved by switching different passive filter structures on and off via switch 24, which connects different filter inductors 25 and filter capacitors 26 to the circuit, and the source impedance Z is also considered. S and load impedance Z L Impedance matching is performed to form common-mode or differential-mode passive EMI filters of different structural types, such as C-type, L-type, Γ-type, inverse Γ-type, T-type, and Π-type. The method for impedance matching of the passive EMI filter filtering environment in passive filter module 20 is shown in Table 2.

[0139] Table 2 Impedance Matching Methods for Passive EMI Filter Filtering Environment

[0140]

[0141]

[0142] For example, when a passive EMI filter is needed to filter differential-mode conducted electromagnetic interference in a power supply device, the resulting source impedance Z... S Approaching 0, load impedance Z L If the value is close to 0, then a T-type differential-mode passive EMI filter will be selected. Students will close switches S3, S4, S5, S6, and S7, and open switches S1, S2, S8, S9, S10, S11, and S12 to achieve this. The selection method is the same for other passive filters.

[0143] (3) Design of active filter module 21: Active filter module 21 is an active EMI filter based on operational amplifier OPA656, with detection network 27, operational network 28 and injection network 29. Voltage detection is selected for the detection network, and current injection is selected for the injection network.

[0144] (4) Design of Digital Active Filter Module 22: The digital active filter module 22 is a digital active EMI filter based on FPGA module 33, featuring a detection network 27, an ADC module 30, a DAC module 32, an amplification network 33, and an injection network 29. The FPGA module 31 is model EP4CE10F1717, the ADC module 30 is model LTC2240, the DAC module 32 is model AD9742, and the amplification network 33 is model OPA847.

[0145] The method of using the experimental device for measuring and filtering conducted electromagnetic interference (EMI) in power supply equipment according to this invention is implemented according to the following steps: For the experimental teaching of the influencing factors of conducted EMI, the student connects the PE switching module 15 to put the conducted EMI experimental module 1 in the grounded mode, and disconnects the PE switching module 15 to put the conducted EMI experimental module 1 in the ungrounded mode. The student changes the voltage of the test object by rotating the duty cycle adjuster 18 and changes the switching frequency of the test object by rotating the switching frequency adjuster 19. The student connects different loads by pressing different load switching switches 16, thereby changing the power of the test object. The changes in grounding and ungrounding, as well as the changes in the test object, demonstrate the conducted EMI of the power supply equipment under different operating conditions to the student. For the measurement and display of conducted EMI, the student controls the EMI measurement module 2 to measure the conducted EMI spectrum through the computer 3, and the measurement results are displayed in the computer's host computer software. The student selects the conducted EMI spectrum waveform to be measured by toggling the filter mode switching switch 17.

[0146] For filter performance testing experiments, after learning about conducted EMI emission measurement in power supply equipment, students need to learn methods for suppressing conducted EMI and the suppression capabilities of different filters. Under different operating conditions of the power supply equipment, different filter modules are connected to the experimental system by toggling the filter module switch 23. Students can learn about the filtering capabilities and characteristics of passive EMI filters, active EMI filters, and digital active EMI filters, as well as the mixed filtering capabilities of passive and active, digital and analog filters. When the switched filter contains a passive filter module, the passive filter module switch 24 is used to adjust to different types of passive EMI filters for different circuits. Students can learn about the differences in filtering capabilities between different types of passive EMI filters.

[0147] Based on this, the present invention designs a teaching experimental device for measuring and filtering conducted electromagnetic interference of power supply equipment. It has a quantitative design method for cable layout and a hybrid EMI filter design that takes into account the source and load impedance characteristics of the filtered object. It can demonstrate the electromagnetic interference emission mechanism of power supply equipment and the insertion loss and other performance of EMI filters, so as to meet the needs of practical teaching courses for electrical engineering majors in colleges and universities.

Claims

1. A teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment, characterized in that: It includes a conducted EMI test platform (4), on which a conducted EMI test module (1), a conducted EMI measurement module (2), and a computer (3) are connected in sequence. The conducted EMI test module (1) includes a measurement board (34), a filtering board (35), and a power load board (36) connected in sequence. The filter module (35) includes a filter module (6), the input end and the output end of the filter module (6) are respectively connected to a slide (13), and three wire clips (14) are provided at equal intervals on each slide (13). The power load module (36) includes a test subject module (7), the positive and negative lines of the DC power line in the test subject module (7) are connected to the load module (8), the test subject module (7) is connected to one end of the controller (9), the other end of the controller (9) is connected to the duty cycle regulator (18) and the switching frequency regulator (19) respectively, and a wire clamp (14) is installed between the test subject module (7) and the controller (9) to fix the signal line. The wire clamp (14) is installed on the slide (13).

2. The teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment according to claim 1, characterized in that: The measurement module (34) includes two impedance stabilizers (5). The L and N AC power lines are connected to the two impedance stabilizers (5) respectively. The PE line is first connected to the PE switching module (15) and then connected to the two impedance stabilizers (5). One end of each of the two impedance stabilizers (5) is connected to one end of the filter mode switching module (10). The other end of the filter mode switching module (10) is the OUT output terminal.

3. The teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment according to claim 2, characterized in that: The load module (8) includes n load resistors (11) and n load switching switches (16), and each load resistor (11) is connected in series with a load switching switch (16).

4. The teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment according to claim 3, characterized in that: The filter module (6) includes parallel L1, N1, and PE1 lines. A passive filter module (20) is connected in series on the L1, N1, and PE1 lines. An active filter module (21) and a digital active filter module (22) are also connected in parallel on the L1, N1, and PE1 lines. A filter mode switching switch (23) is provided at both ends of the passive filter module (20). A filter mode switching switch (23) is provided on the connection lines between the active filter module (21) and the digital active filter module (22) and the L1, N1, and PE1 lines.

5. The design method of the teaching experimental device for measuring and filtering conducted electromagnetic interference of power supply equipment according to any one of claims 1 to 4, characterized in that: This includes the distance between the conducted EMI experimental platform (4), the impedance stabilizer (5), and the test subject module (7). The spacing design of the wire clamp (14).

6. The design method of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment according to claim 5, characterized in that: The platform height of the conducted EMI test platform (4) h The design process is as follows: Based on the capacitive coupling mechanism of power supply devices, parasitic capacitance is generated between the power supply device and the metal base plate through the switching transistor. The platform height of the conductive EMI test platform (4) h With the parasitic capacitance The relevant formula is: （1） in, It is the vacuum permittivity; It is the relative permittivity; For the length of the power supply equipment; The width of the power supply equipment; based on the common-mode noise loop formed by the power supply equipment and the impedance stabilizer, the common-mode noise loop satisfies the following equation: （2） in, This is the common-mode interference source voltage; This is the common-mode interference current; This refers to the internal resistance of the impedance stabilizer; This is the internal capacitor of the impedance stabilizer; This refers to the parasitic capacitance between the switching transistor and the metal base plate. This is the switching frequency of the switching transistor; The platform height of the conducted EMI test platform (4) h The following relationship must be satisfied: （3）； The distance from the conducted EMI experimental module (1) to the rear side metal plate is x Based on the capacitive coupling mechanism of the power supply equipment, a common-mode noise circuit is constructed. According to formulas (1) to (3), we can obtain... x The size satisfies: （4） in, The distance between the power supply equipment and the wall; The distance between the impedance stabilizer (5) and the subject module (7) The design process is as follows: Based on the principle of conducted coupling, the PE line is shared in the common-mode circuits of both the L line and the N line. When there is interference current in the L line, the interference voltage generated on the L line will affect the N line, resulting in conducted coupling. According to the equivalent circuit of conducted coupling in the common-mode loop of the L line, the following formula (5) is obtained: （5） in, This refers to crosstalk between the L line and the PE line. This is the common-mode interference source voltage; The load impedance between the L line and the PE line; This is the load impedance between the N-line and the PE-line; The source impedance between the L line and the PE line; The source impedance between the N-line and the PE-line; The impedance of the PE line; PE line impedance The distance between the impedance stabilizer (5) and the subject module (7) Related to this impedance Expressed using formula (6): （6） in, The resistivity of the conductor; The distance between the impedance stabilizer (5) and the subject module (7) is obtained according to formulas (5) and (6). for: （7） in, This refers to crosstalk between the L line and the PE line. The load impedance between the L line and the PE line. This is the load impedance between the N-line and the PE-line. The source impedance between the N-line and the PE-line. ρ is the resistivity of the conductor.

7. The design method of the teaching experimental device for measuring and filtering conducted electromagnetic interference in power supply equipment according to claim 6, characterized in that: The design process for the spacing of the wire clamp (14) is as follows: The input and output terminals of the filter module (6) are respectively connected to a set of slides (13). Three wire clamps (14) are equidistantly arranged in each set of slides (13). At this time, the two sets of slides (13) and their corresponding three wire clamps (14) constitute H1 and H2. Among them, H1 is located between the impedance stabilizer (5) and the filter module (6); H2 is located between the filter module (6) and the subject module (7). The distance between the L line and the N line is adjusted by moving the wire clamps (14) on the slides (13). The distance between line L and line N The design process is as follows: Based on the electric field coupling theory, when common-mode noise voltage is present, the L-line and N-line will generate a coupling capacitance when they are close to each other. This leads to crosstalk between the L line and the N line. Based on the equivalent circuit of the capacitive coupling between the L line and the N line, the following formula (8) is obtained: （8） in, This refers to crosstalk between the L line and the N line. The load impedance between the L line and the PE line; This is the load impedance between the N-line and the PE-line; The source impedance between the L line and the PE line; The source impedance between the N-line and the PE-line; The capacitance of line L to ground; This refers to the capacitance between the neutral (N) line and ground. This is the coupling capacitance between the L line and the N line; This is the switching frequency of the switching transistor; According to the principle of interconductor capacitance, the L-line and N-line generate coupling capacitance at high frequencies. Spacing between the two lines Regarding the capacitor Expressed using formula (9): （9） in, is the dielectric constant of air; The spacing between the L line and the N line; The distance between the impedance stabilizer and the subject module; Let be the radius of the conductor; According to the principle of a parallel-plate capacitor, the L-line and N-line generate an L-line-to-ground capacitance at high frequencies. and an N-line to ground capacitor The height of these two capacitors relative to the platform of the conducted EMI test platform h Related to capacitors and Expressed using formula (10): （10） in, The distance between the impedance stabilizer and the subject module; Let L be the radius of the conductor; the distance between L and N is obtained according to formulas (8) to (10). for: （11） in: （12） This is the crosstalk between the L line and the N line. It is the relative permittivity; The load impedance between the L line and the PE line. The source impedance between the L line and the PE line. The switching frequency of the switching transistor; to balance the common-mode interference between the L and N lines, the distances from the PE line to the L line and from the PE line to the N line are: ; A wire clamp (14) is installed between the subject module (7) and the controller (9) to fix the signal line. The wire clamp (14) is installed on the slide (13) to form H3. The distance between the signal line of the controller (9) and the power supply line is adjusted by moving the wire clamp (14) on the slide (13). Based on the electric field coupling theory, the distance between the controller's signal line and the power supply line can be obtained according to formulas (8) to (12). The following relationship must be satisfied: （13） （14）。

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