Voltage detection current injection type AEF using weak positive feedback to adjust capacitance value of Y capacitor

Abstract

The invention belongs to the technical field of electromagnetic interference filtering, and relates to a voltage detection current injection type AEF for adjusting the capacitance value of a Y capacitor by using weak positive feedback, which comprises a Y capacitor capacitance value adjusting circuit and an RC series branch, the Y capacitor capacitance value adjusting circuit can effectively adjust the capacitance value of the capacitor, so that a large capacitor is obtained for common-mode noise filtering, the effect of the large capacitor can be obtained by using a small capacitor, and common-mode electromagnetic interference is better inhibited; the Y capacitor capacitance adjusting circuit is composed of two CY capacitors to be amplified, two positive feedback resistors, an operational amplifier, a negative feedback capacitor and a negative feedback stabilizing resistor, and after the Y capacitor capacitance adjusting circuit is connected with the capacitors to be amplified in series, common-mode equivalent impedance is greatly reduced, a low-impedance loop is constructed for electromagnetic interference, and therefore conduction of the electromagnetic interference is restrained. Meanwhile, the capacitance value of the capacitor can be accurately adjusted, and high flexibility is achieved; and the RC series branch comprises a resistor and a capacitor, and the output voltage of the operational amplifier is coupled with the bus, so that the voltage is converted into current compensation, and the common-mode filtering effect is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic interference filtering, and relates to a voltage detection current injection type AEF that utilizes weak positive feedback to adjust the capacitance of a Y capacitor. Background Art

[0002] At present, with the development of power electronics technology, the demand for high efficiency and high power density design is growing. Wide bandgap devices have higher critical electric fields, higher saturation drift speeds, higher electron mobility (gallium nitride) and higher thermal conductivity (silicon carbide), and play an increasingly important role in power electronics systems. However, with the continuous development of wide bandgap power semiconductors, their high switching speeds and higher switching frequencies have effectively improved the power density, but have brought new challenges, among which electromagnetic interference (EMI) is one of the main problems. Severe electromagnetic interference may interfere with the normal operation of the equipment and even have serious self-compatibility problems. For the electromagnetic interference problem, a common solution is to add an EMI filter and use inductors and capacitors to build a passive EMI filter to block the conduction of EMI noise on the line.

[0003] However, passive filters often require large inductance and capacitance parameters to achieve the filtering effect required for low frequencies, otherwise the EMI noise at the resonance point may increase instead of decrease. Large inductance will lead to a larger EMI filter, and it may even be larger than the power electronic converter, which is not in line with the trend of miniaturization and lightweighting of power electronic devices. For common mode capacitors, their values ​​are limited by safety regulations and it is difficult to take a larger value.

[0004] Therefore, a device or method is needed to obtain a larger common-mode capacitor without increasing the volume, thereby effectively reducing the inductance and capacitance parameters of the EMI filter and improving the filtering effect to solve the above technical problems. Summary of the invention

[0005] The present invention uses a voltage detection current injection type AEF that uses weak positive feedback to adjust the capacitance of the Y capacitor, adjusts the capacitance on the basis of a small common mode capacitor, and can adjust the capacitance parameters without increasing the inductance and capacitance parameters, thereby achieving a better common mode filtering effect, and is combined with a traditional voltage detection current injection type AEF to achieve a better common mode filtering effect. Therefore, the present invention can obtain a larger common mode capacitor without increasing the volume, and at the same time convert the noise voltage into current compensation, which can effectively reduce the inductance and capacitance parameters of the EMI filter and improve the filtering effect.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a voltage detection current injection type AEF that uses weak positive feedback to adjust the capacitance of a Y capacitor, including: a Y capacitor capacitance adjustment circuit, an RC series branch;

[0007] The Y capacitor capacitance adjustment circuit amplifies the sampled noise voltage by introducing a positive feedback loop;

[0008] The RC series branch converts the common-mode noise voltage into a compensation current, further suppressing the common-mode noise.

[0009] Preferably, the Y capacitor capacitance adjustment circuit comprises: a first Y capacitor, a second Y capacitor, a first positive feedback resistor, a second positive feedback resistor, an operational amplifier, a negative feedback capacitor, and a negative feedback stabilizing resistor;

[0010] The circuit connection method of the Y capacitor capacitance adjustment circuit includes: a first Y capacitor and a second Y capacitor are connected in series, a common end of the first Y capacitor and the second Y capacitor after being connected in series is connected to the inverting input end of the operational amplifier, and terminals at both ends of the first Y capacitor and the second Y capacitor after being connected in series are respectively connected to the positive and negative busbars of the noise source device; the non-inverting input end of the operational amplifier is connected to the first positive feedback resistor, and the other end of the first positive feedback resistor is grounded; the non-inverting input end and the output end of the operational amplifier are respectively connected to the two ends of the second positive feedback resistor; the inverting input end and the output end of the operational amplifier are respectively connected to the two ends of the negative feedback capacitor and the two ends of the negative feedback stabilization resistor;

[0011] The RC series branch includes: a first capacitor, a first resistor, a second capacitor, and a second resistor;

[0012] The circuit connection method of the RC series branch includes: the first capacitor, the first resistor, the second capacitor, and the second resistor are sequentially connected in series, and the terminals at both ends are respectively connected to the positive and negative busbars of the noise source device;

[0013] A common end of the first resistor and the second capacitor connected in series is connected to the output end of the operational amplifier.

[0014] More preferably, the first Y capacitor and the second Y capacitor each include a group of Y capacitors connected in series or in parallel.

[0015] Preferably, the capacitance values ​​of the first Y capacitor and the second Y capacitor are equal; Y The capacitors are two capacitors with the same capacitance, and multiple capacitors can be connected in parallel to reduce parasitic parameters, and suitable reference capacitors can be selected for amplification, making it easier to achieve good noise suppression effects, wherein the point-connected capacitor capacitance adjustment circuit.

[0016] Preferably, the voltage detection current injection type AEF is also circuit-connected with LISN and EUT on both sides respectively; the left side of the circuit is the input power supply and LISN, i.e., the artificial power supply network; the right side is the EUT, i.e., the corresponding power electronic converter noise source, which forms feedback through the AEF to weaken common-mode electromagnetic interference.

[0017] More preferably, the voltage detection current injection type AEF has a positive feedback amplification factor of 1+R b / R a When , the external equivalent impedance of the operational amplifier circuit composed of the first positive feedback resistor, the second positive feedback resistor, the operational amplifier, the negative feedback capacitor, and the negative feedback stabilizing resistor includes:

[0018]

[0019] In formula (3), V in It represents the inverting input voltage of the operational amplifier, I in represents the current flowing through the negative feedback RC network, Z CF Represents the negative feedback capacitor impedance, R a , R b Respectively represent the resistance values ​​of the first positive feedback resistor and the second positive feedback resistor;

[0020] When the first positive feedback resistor and the second positive feedback resistor connected to the operational amplifier are adjusted, the equivalent common-mode impedance is determined by equation (6):

[0021]

[0022] In formula (6), V CM Indicates the bus common mode noise voltage at the parallel point, I CM Represents the current flowing through the Y capacitor, C Y Indicates the capacitance value of the Y capacitor, C F represents the capacitance value of the negative feedback capacitor, s represents a complex frequency variable, which is used to represent the equivalent impedance;

[0023] After two positive feedback resistors R a and R b Adjusting the weak positive feedback coefficient can adjust the EMI filtering effect, which is flexible in practical applications. At this time, a low impedance loop is constructed for the electromagnetic interference noise, which can effectively suppress the conduction of the electromagnetic interference noise. The two positive feedback resistors R a and R b The ratio is controlled to keep the negative feedback and positive feedback of the operational amplifier balanced. When the positive feedback is too large, it will cause instability of the operational amplifier, which will lead to self-oscillation and introduce additional noise. The filtering effect of the AEF circuit can be further adjusted by utilizing its weak positive feedback.

[0024] Preferably, the negative feedback capacitor is composed of multiple capacitors connected in parallel; the negative feedback capacitor composed of multiple capacitors connected in parallel can reduce parasitic parameters and perform impedance adjustment in combination with the positive feedback resistor; the negative feedback stabilizing resistor provides a feedback loop for the DC, i.e., low-frequency voltage, to prevent low-frequency circuit instability. On the other hand, due to the large insulation resistance of the capacitor, the parallel negative feedback resistor can provide a loop for the operational amplifier to avoid DC saturation.

[0025] More preferably, the relationship between the output voltage of the operational amplifier and the common mode noise voltage includes:

[0026]

[0027] In formula (7), V out Represents the output voltage of the operational amplifier; at this time, the output voltage is the reverse amplification of the bus common-mode noise voltage, and the amplification factor is large, the compensation effect is good, and the EMI suppression efficiency is higher; the capacitor of the RC series branch is used to isolate the bus voltage, and the capacitance is large. In the conducted noise range, the impedance of the RC series branch can be mainly provided by the resistor, and the output voltage of the operational amplifier is converted into current compensation, which can improve the EMI filtering effect; the absolute value of the impedance of the capacitor to be amplified needs to be slightly larger than the absolute value of the external equivalent impedance of the operational amplifier circuit composed of the first positive feedback resistor, the second positive feedback resistor, the operational amplifier, the negative feedback capacitor, and the negative feedback stabilization resistor, otherwise the circuit will become positive feedback, resulting in instability.

[0028] The beneficial effects of the present invention are:

[0029] 1. The present invention improves the problem that it is difficult to use large capacitors in EMI filters. The capacitor is equivalently increased in an active manner. Compared with traditional passive EMI filters, the ability to suppress common-mode EMI noise is effectively improved while reducing the size of the filter.

[0030] 2. The present invention can accurately adjust the capacitance value of the capacitor. The effect of the amplified capacitor is similar to that of the actual capacitor with the same capacitance value. It can be adjusted as needed and has a better filtering effect for the low frequency band.

[0031] 3. The present invention adds an RC series branch on the basis of adjustable capacitance, and the compensation effect of the RC series branch increases with the increase of the capacitance amplification factor, thereby providing a better compensation effect on the basis of a large equivalent capacitance and further suppressing EMI noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a circuit diagram of a voltage detection current injection type AEF of the present invention that uses weak positive feedback to adjust the capacitance of the Y capacitor;

[0033] Figure 2It is a schematic diagram of the use scenario of the voltage detection current injection type AEF of the present invention which uses weak positive feedback to adjust the capacitance of the Y capacitor;

[0034] Figure 3 It is a comparison diagram of the spectrum of the bare noise of the present invention and the noise after adopting the filter.

[0035] Among them, 101a is a first Y capacitor; 101b is a second Y capacitor; 102a is a first positive feedback resistor; 102b is a second positive feedback resistor; 103 is an operational amplifier; 104 is a negative feedback capacitor; 105 is a negative feedback stabilizing resistor; 106 is a first capacitor; 107 is a first resistor; 108 is a second capacitor; and 109 is a second resistor. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] refer to Figure 1 The voltage detection current injection type AEF for adjusting the capacitance of the Y capacitor proposed in this embodiment includes a Y capacitor capacitance adjustment circuit and an RC series branch. The Y capacitor capacitance adjustment circuit includes a resistor, a capacitor and an operational amplifier. By introducing a positive feedback loop to amplify the noise voltage obtained by sampling, the common mode impedance after series connection can be effectively reduced, so that the equivalent capacitance value is increased, and the common mode filtering effect is effectively improved without changing the volume. The capacitance value can be accurately adjusted by adjusting the positive feedback coefficient and parameter design, which has adjustability and greater flexibility, and reduces the demand for large common mode inductance. Secondly, since the output voltage of the operational amplifier is the reverse amplification of the noise voltage, an RC series branch is introduced on this basis to convert the common mode noise voltage into a compensation current to further suppress the common mode noise. The Y capacitor capacitance adjustment circuit is coupled with the earth to form the equivalent of a large capacitance common mode capacitor, and the RC series branch is drawn out at the output end of the operational amplifier to connect to the DC positive and negative busbars to provide a compensation current. This embodiment can be connected in parallel between the input power supply and the power electronic converter to provide a low impedance loop for the common mode noise, effectively suppress the conduction of the electromagnetic interference noise at the input end, and significantly reduce the leakage current.

[0038] In the circuit of this embodiment, the voltage detection current injection type AEF that uses weak positive feedback to adjust the capacitance of the Y capacitor includes a Y capacitor capacitance adjustment circuit and an RC series branch. The Y capacitor capacitance adjustment circuit can adjust the Y capacitor capacitance according to the adjustment of the positive feedback loop, so that the common mode filtering effect is equivalently increased without changing the volume, and a low impedance loop is provided for the common mode noise to suppress its conduction, and it has adjustability and greater flexibility. The output of the operational amplifier is a reverse amplification of the noise voltage, which is connected to the positive and negative busbars through resistors and capacitors to convert the noise voltage into a current compensation signal to further suppress EMI noise. The AEF is connected in parallel between the power input and the power electronic converter to form a common mode filter. The Y capacitor capacitance adjustment circuit includes a capacitor resistor and an operational amplifier, and the operational amplifier can amplify the noise voltage sampled at the midpoint to form a low impedance loop, so that the capacitance is equivalently amplified, and the RC series branch circuit includes a resistor capacitor, and the capacitor impedance is small within the frequency range of the conducted noise, so that the impedance after the series connection can be mainly provided by the resistor.

[0039] The composition, main principles, use methods and use effects of the present invention are described in detail below in conjunction with the accompanying drawings of the embodiments of the present invention.

[0040] Example

[0041] refer to Figure 1 The voltage detection current injection type AEF proposed in this embodiment uses weak positive feedback to adjust the capacitance of the Y capacitor. The circuit includes:

[0042] The voltage detection current injection type AEF that uses weak positive feedback to adjust the Y capacitor capacitance includes a Y capacitor capacitance adjustment circuit and an RC series branch. The two ends of the entire AEF are connected in parallel between the input power supply and the power electronic converter. The Y capacitor capacitance adjustment circuit includes a capacitor resistor and an operational amplifier 103, where C Y The capacitor to be amplified is two Y capacitors with the same capacitance connected in series, namely the first Y capacitor 101a and the second Y capacitor 101b, with a total of 3 terminals, C Y The common terminal is connected to the inverting input terminal of the operational amplifier, and the other two terminals are connected to the positive and negative busbars of the noise source device respectively. a and R b The positive feedback loop resistors, namely the first positive feedback resistor 102a and the second positive feedback resistor 102b, are used to adjust the capacitance value, and the negative feedback stabilization resistor R F , that is, the negative feedback stabilizing resistor 105, provides a loop for the input bias current and DC feedback of the op amp, and the negative feedback capacitor C F , that is, negative feedback capacitor 104, is used to adjust the external equivalent impedance and to communicate with R FIn parallel, within the frequency range of conducted noise, the impedance of the resistor is larger than that of the capacitor, and the impedance of the two in parallel can be approximated as the impedance of the capacitor. The non-inverting input terminal of the operational amplifier 103 is connected to the ground with a positive feedback resistor R a , and the output of the operational amplifier 103 through the positive feedback resistor R b The inverting input terminal of the operational amplifier 103 is connected to the C Y The capacitor midpoint is connected to the output of the operational amplifier 103 through the negative feedback capacitor C F connection, where the capacitor is connected with a negative feedback stabilization resistor R F The Y capacitor capacitance adjustment circuit is connected in parallel by Y The midpoint voltage of the operational amplifier 103 is sampled and amplified, so that the impedance of the common-mode loop after the series connection is reduced by a certain proportion, and thus equivalent to a capacitor with a larger capacitance. Therefore, the circuit can achieve precise adjustment of the capacitance value, obtain a larger common-mode insertion loss on the basis of unchanged volume, and better suppress the conducted common-mode noise. The output end of the operational amplifier 103 is connected to the common node of the RC series branch, and the RC series branch is connected by a resistor R S and capacitor C S The capacitor is used to isolate the bus voltage, and the capacitance is large. In the range of conducted noise, the impedance of the series branch can be mainly provided by the resistor. The two ends of the two series branches are connected to the positive bus and negative bus of the power supply system respectively. Using the output voltage of the op amp for compensation can improve the EMI filtering effect. Y The capacitor side is the input power line port. The side close to the resistor-capacitor series branch is the noise source device. Figure 1 The capacitance value of the capacitor after adjustment can be calculated. First, the external equivalent impedance of the Y capacitor capacitance adjustment circuit is calculated. The output voltage of the operational amplifier 103 is shown in formula (1), where V out is the operational amplifier output voltage, V in is the voltage at the inverting input of the operational amplifier.

[0043]

[0044] Based on the impedance between the input and output terminals of the op amp, the input current expression can be obtained as shown in formula (2), where I in is the current flowing into the negative feedback resistor-capacitor parallel network, Z CF is the capacitance impedance between the op amp inverting terminal and the output, Z CY is the impedance of the capacitor to be amplified. The resistor R in parallel with the capacitor F In the range of conducted noise, the impedance is large compared to the capacitance and can be ignored.

[0045]

[0046] Substituting (1) into (2), we can calculate the external equivalent expression of the operational amplifier circuit, as shown in formula (3).

[0047]

[0048] By writing the current equation for the bus and the inverting input terminal of the op amp at the same time, the input current expression of the op amp circuit can be calculated, as shown in equation (4), where V CM is the bus common mode noise voltage at the parallel point.

[0049] 2S Y (V CM -V in )=I in =2I CM (4)

[0050] Substituting equation (3) into equation (4) yields the relationship between the common-mode input current and the bus common-mode noise voltage, as shown in equation (5), where I CM is connected in parallel to the capacitor C to be amplified Y of common mode current.

[0051]

[0052] The equivalent impedance to ground can be obtained by transforming equation (5) as shown in equation (6), where Z CM is the equivalent common mode impedance.

[0053]

[0054] At this time, the common-mode equivalent impedance of the circuit can be obtained by the two positive feedback resistors R a and R b The resistance value of the amplified capacitor C is precisely controlled to achieve Y The precise amplification of the common mode current builds a low impedance loop, which can effectively suppress the conduction of common mode electromagnetic interference noise. The positive feedback effect needs to be weaker than the negative feedback branch to prevent the operational amplifier from self-oscillating. The weak positive feedback effect can be used to further adjust the filtering effect of the AEF circuit.

[0055] By analyzing the RC series branch, the input voltage of the inverting terminal of the operational amplifier can be calculated using the equivalent impedance voltage divider, as shown in formula (7).

[0056]

[0057] The output voltage of the operational amplifier is the reverse amplification of the bus common mode voltage. When the capacitance amplification factor is large, the weak positive feedback coefficient can be controlled to make the capacitor C to be amplified YThe absolute value of the impedance is slightly larger than the absolute value of the external equivalent impedance of the operational amplifier circuit composed of the first positive feedback resistor, the second positive feedback resistor, the operational amplifier, the negative feedback capacitor, and the negative feedback stabilization resistor after weak positive feedback adjustment, so that the denominator is positive, and the output voltage of the operational amplifier is the reverse amplified common mode noise voltage. At this time, the denominator is smaller than the numerator modulus, and a larger amplification factor can be obtained, thereby converting the noise voltage into a large compensation current to better suppress EMI noise conduction. Weak positive feedback changes the equivalent impedance and provides feedback voltage.

[0058] Figure 2 This is a typical voltage detection current injection AEF usage scenario that uses weak positive feedback to adjust the capacitance of the Y capacitor. In this circuit diagram, L and C Y2 For passive filtering, R Y2 It is used to provide damping to enhance high-frequency stability. The common-mode inductor has a small inductance and capacitance, so it is small in size and is mainly used to filter high-frequency noise. The voltage detection current injection type AEF that uses weak positive feedback to adjust the capacitance of the Y capacitor is close to the noise source. The power electronic converter is the EMI noise source, and the artificial power supply network is used to detect common-mode noise. Following the impedance mismatch principle, when the source impedance is large, the AEF is connected in parallel first and then the common-mode inductor is connected in series, which can make the low-frequency electromagnetic interference suppression effect better. A low-impedance loop can be constructed through the common-mode Y capacitor capacitance adjustment circuit, and the inductor constructs a high-impedance loop to suppress the propagation of electromagnetic interference noise. Further compensation on this basis can obtain a better suppression effect.

[0059] Figure 3 The figure is a comparison of filtering effects, that is, the comparison between the AEF of the present invention and naked noise. Figure 3 (a) is the circuit bare noise, Figure 3 (b) is the common-mode noise spectrum of the hybrid EMI filter with AEF. It can be seen that the proposed AEF has a significant suppression effect on common-mode electromagnetic interference noise.

[0060] Abbreviations in this embodiment

[0061] AEF Active EMI filter

[0062] EMI Electromagnetic Interference

[0063] LISN Line Impedance Stabilization Network Line Impedance Stabilization Network

[0064] EUT Equipment Under Test

[0065] In summary, the present invention improves the problem of difficulty in using large capacitors in EMI filters, and increases the capacitance equivalently in an active manner. Compared with traditional passive EMI filters, the ability to suppress common-mode EMI noise is effectively improved while reducing the volume of the filter; the present invention accurately adjusts the capacitance value, and the amplified capacitance has a similar effect to the actual use of the same capacitance value capacitor, which can be adjusted as needed, and has a better filtering effect for low-frequency bands. Therefore, the present invention can obtain a larger common-mode capacitor without increasing the volume, thereby effectively reducing the inductance and capacitance parameters of the EMI filter and improving the filtering effect.

[0066] It should be emphasized that the above are only preferred embodiments of the present invention and do not impose any form of limitation on the present invention. Any simple modification of the above embodiments based on the technical essence of the present invention also falls within the protection scope of the present invention. Other equivalent changes and modifications still fall within the scope of the technical solution of the present invention.

Claims

1. A voltage detection current injection type AEF that uses weak positive feedback to adjust the capacitance of the Y capacitor, characterized in that: include: Y capacitor capacitance adjustment circuit, RC series branch; The Y capacitor capacitance adjustment circuit amplifies the noise voltage obtained by sampling by introducing a positive feedback loop; The RC series branch converts the common mode noise voltage into a compensation current, thereby further suppressing the common mode noise.

2. The voltage detection current injection type AEF using weak positive feedback to adjust the capacitance of the Y capacitor according to claim 1, characterized in that: The Y capacitor capacitance adjustment circuit comprises: a first Y capacitor (101a), a second Y capacitor (101b), a first positive feedback resistor (102a), a second positive feedback resistor (102b), an operational amplifier (103), a negative feedback capacitor (104), and a negative feedback stabilizing resistor (105); The circuit connection method of the Y capacitor capacitance adjustment circuit includes: a first Y capacitor (101a) and a second Y capacitor (101b) are connected in series, the common end of the first Y capacitor (101a) and the second Y capacitor (101b) are connected in series to the inverting input end of an operational amplifier (103), and the two ends of the first Y capacitor (101a) and the second Y capacitor (101b) are respectively connected to the positive and negative busbars of a noise source device; the non-inverting input end of the operational amplifier (103) is connected to the first positive feedback resistor (102a), and the other end of the first positive feedback resistor (102a) is grounded; the non-inverting input end and the output end of the operational amplifier (103) are respectively connected to the two ends of the second positive feedback resistor (102b); the inverting input end and the output end of the operational amplifier (103) are respectively connected to the two ends of a negative feedback capacitor (104) and the two ends of a negative feedback stabilization resistor (105); The RC series branch includes: a first capacitor (106), a first resistor (107), a second capacitor (108), and a second resistor (109); The circuit connection method of the RC series branch includes: a first capacitor (106), a first resistor (107), a second capacitor (108), and a second resistor (109) are sequentially connected in series, and the two ends are respectively connected to the positive and negative busbars of the noise source device; The common end of the first resistor (107) and the second capacitor (108) connected in series is connected to the output end of the operational amplifier (103).

3. The voltage detection current injection type AEF using weak positive feedback to adjust the capacitance of the Y capacitor according to claim 2, characterized in that: The first Y capacitor (101a) and the second Y capacitor (101b) respectively include a group of Y capacitors connected in series or in parallel.

4. The voltage detection current injection type AEF using weak positive feedback to adjust the capacitance of the Y capacitor according to claim 2, characterized in that: The capacitance values ​​of the first Y capacitor (101a) and the second Y capacitor (101b) are equal.

5. The voltage detection current injection type AEF using weak positive feedback to adjust the capacitance of the Y capacitor according to claim 2, characterized in that: The two sides of the voltage detection current injection type AEF are also circuit-connected with LISN and EUT respectively.

6. The voltage detection current injection type AEF using weak positive feedback to adjust the capacitance of the Y capacitor according to claim 2, characterized in that: The voltage detection current injection type AEF has a positive feedback amplification factor of 1+R b / R a When , the operational amplifier circuit composed of the first positive feedback resistor (102a), the second positive feedback resistor (102b), the operational amplifier (103), the negative feedback capacitor (104), and the negative feedback stabilizing resistor (105) has an external equivalent impedance including: In formula (3), V in represents the inverting input voltage of the operational amplifier (103), I in represents the current flowing through the negative feedback RC network, Z CF represents the impedance of the negative feedback capacitor (104), R a , R b Respectively represent the resistance values ​​of the first positive feedback resistor (102a) and the second positive feedback resistor (102b); When the first positive feedback resistor (102a) and the second positive feedback resistor (102b) connected to the operational amplifier (103) are adjusted, the equivalent common mode impedance is determined by equation (6): In formula (6), V CM Indicates the bus common mode noise voltage at the parallel point, I CM Represents the current flowing through the Y capacitor, C Y Indicates the capacitance value of the Y capacitor, C F represents the capacitance value of the negative feedback capacitor (104), and s represents a complex frequency variable.

7. The voltage detection current injection type AEF using weak positive feedback to adjust the capacitance of the Y capacitor according to claim 2, characterized in that: The negative feedback capacitor (104) is composed of a plurality of capacitors connected in parallel.

8. The voltage detection current injection type AEF using weak positive feedback to adjust the capacitance of the Y capacitor according to claim 2, characterized in that: The relationship between the output voltage of the operational amplifier (103) and the common mode noise voltage includes: In formula (7), V out represents the output voltage of the operational amplifier (103).

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