Voltage detection current injection type aef with weak positive feedback to adjust y capacitance value

Abstract

The application belongs to the technical field of electromagnetic interference filtering, and relates to a voltage detection current injection type AEF using weak positive feedback to adjust the capacitance value of Y capacitor, which comprises a Y capacitor capacitance value adjusting circuit and an RC series branch. Y The Y capacitor capacitance value adjusting circuit can effectively adjust the capacitance value, so that a large capacitor is obtained for common mode noise filtering, a small capacitor can be used to obtain the effect of a large capacitor, and common mode electromagnetic interference is better inhibited; the Y capacitor capacitance value adjusting circuit is composed of two to-be-amplified capacitors C Y , two positive feedback resistors, an operational amplifier, a negative feedback capacitor and a negative feedback stabilizing resistor, which are connected in series with the to-be-amplified capacitors, greatly reduce the common mode equivalent impedance, build a low impedance loop for electromagnetic interference, so as to inhibit the conduction of electromagnetic interference; meanwhile, the capacitance value can be accurately adjusted, and the flexibility is large; the RC series branch comprises a resistor and a capacitor, which couple the output voltage of the operational amplifier with the bus, so as to convert the voltage into current compensation, and further improve the common mode filtering effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic interference filtering, and relates to a voltage detection current injection type AEF using weak positive feedback to adjust the capacitance value of Y capacitor. BACKGROUND

[0002] At present, with the development of power electronic technology, the demand for high efficiency and high power density design is increasing. Wide bandgap devices have higher critical electric field, higher saturation drift velocity, higher electron mobility (gallium nitride) and higher thermal conductivity (silicon carbide), and play an increasingly important role in power electronic systems. However, with the continuous development of wide bandgap power semiconductors, although the high switching speed and higher switching frequency effectively improve the power density, it brings new challenges, one of which is electromagnetic interference (EMI). Serious electromagnetic interference may interfere with the normal operation of the equipment, and even have serious self-compatibility problems. For the problem of electromagnetic interference, the common solution is to add an EMI filter to block the conduction of EMI noise on the line using inductors and capacitors.

[0003] However, passive filters often require large inductance and capacitance parameters to achieve the required filtering effect at low frequencies, otherwise the EMI noise may not decrease but increase at the resonance point. Large inductance may result in a large volume of EMI filter, and even the volume of EMI filter may be larger than that of power electronic converter, which does not meet the trend of miniaturization and light weight of power electronic devices. For common mode capacitors, their values are limited by safety regulations and cannot be too large.

[0004] Therefore, a device or method that 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, is needed to solve the above technical problems. SUMMARY

[0005] The application uses weak positive feedback to adjust the voltage detection current injection type AEF of Y capacitor capacitance value, adjusts the capacitance value on the basis of small common mode capacitor, and adjusts the capacitance parameters without increasing the inductance and capacitance parameters, thereby achieving better common mode filtering effect, and combining with the traditional voltage detection current injection type AEF to achieve better common mode filtering effect. Therefore, the application can obtain a larger common mode capacitor without increasing the volume, and 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 application to solve the technical problems is: the voltage detection current injection type AEF using weak positive feedback to adjust the capacitance value of Y capacitor, comprising: a Y capacitor capacitance value adjusting circuit and an RC series branch.

[0007] The Y capacitor value adjusting 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 value adjusting 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 mode of the Y capacitor value adjusting circuit comprises: the first Y capacitor and the second Y capacitor are connected in series, the common end of the first Y capacitor and the second Y capacitor connected to the inverting input terminal of the operational amplifier, and the terminals at both ends of the first Y capacitor and the second Y capacitor connected in series are respectively connected to the positive and negative busbars of the noise source device; the non-inverting input terminal 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 terminal and the output terminal of the operational amplifier are respectively connected to the two ends of the second positive feedback resistor; the inverting input terminal and the output terminal of the operational amplifier are respectively connected to the two ends of the negative feedback capacitor and the two ends of the negative feedback stabilizing resistor.

[0011] The RC series branch comprises: a first capacitor, a first resistor, a second capacitor, and a second resistor.

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

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

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

[0015] More preferably, the capacitance values of the first Y capacitor and the second Y capacitor are equal; the capacitance value of the to-be-amplified C Y The capacitors are two capacitors with consistent capacitance values, and can be composed of multiple capacitors connected in parallel to reduce parasitic parameters, and a suitable reference capacitor can be selected for amplification, which makes it easier to achieve good noise suppression effect, and the point connection capacitor value adjusting circuit.

[0016] More preferably, the voltage detection current injection type AEF is further connected with a LISN and an EUT on both sides; the left side of the circuit is an input power supply and the LISN, i.e., an artificial power supply network; and the right side is the EUT, i.e., a corresponding power electronic converter noise source, which forms a feedback through the AEF to weaken the 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 positive feedback amplification factor is 1+R

[0018]

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

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

[0021]

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

[0023] By adjusting the weak positive feedback coefficient of the two positive feedback resistors R a and R b , the EMI filtering effect can be adjusted, which has flexibility in practical applications. At this time, a low impedance loop is constructed for electromagnetic interference noise, which can effectively suppress the conduction of electromagnetic interference noise. The ratio of the two positive feedback resistors R a and R b needs to be controlled, so that the negative feedback and positive feedback of the operational amplifier remain balanced. When the positive feedback is too large, it will cause the operational amplifier to be unstable, and then cause self-oscillation, introducing additional noise. By utilizing the weak positive feedback effect, the filtering effect of the AEF circuit can be further adjusted.

[0024] More preferably, the negative feedback capacitor is composed of multiple capacitors in parallel; the negative feedback capacitor composed of multiple capacitors in parallel can reduce parasitic parameters and adjust impedance in combination with the positive feedback resistor; the negative feedback stabilizing resistor provides a feedback loop for low-frequency voltage, preventing low-frequency circuit instability; on the other hand, the parallel negative feedback resistor can provide a loop for the operational amplifier due to the large insulation resistance of the capacitor, avoiding DC saturation.

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

[0026]

[0027] In formula (7), V out represents the output voltage of the operational amplifier; at this time, the output voltage is the inverse 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 value is large, which can make the impedance of the RC series branch mainly provided by the resistor in the conducted noise range, convert the output voltage of the operational amplifier into current compensation, and improve the EMI filtering effect; it is necessary to make the absolute value of the to-be-amplified capacitor impedance slightly larger than the absolute value of the 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, otherwise the circuit will become positive feedback, resulting in instability.

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

[0029] 1. The present application improves the problem that large capacitors are difficult to use in EMI filters, and equivalently increases the capacitance in an active manner, compared with traditional passive EMI filters, effectively improves the common-mode EMI noise suppression capability while reducing the size of the filter.

[0030] 2. The present application can accurately adjust the capacitance value, and the amplified capacitor has similar effect to the actual use of the same capacitance value, which can be adjusted as needed, and has good low-frequency band filtering effect.

[0031] 3. The present application increases the RC series branch on the basis of adjustable capacitor, and the compensation effect of the RC series branch increases with the increase of the amplification factor of the capacitor, so as to provide better compensation effect on the basis of large equivalent capacitor, and further suppress EMI noise. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a circuit schematic diagram of the voltage detection current injection type AEF of the present application using weak positive feedback to adjust the Y capacitor capacitance value;

[0033] Figure 2is a use scene schematic diagram of the voltage detection current injection type AEF of the present application using weak positive feedback to adjust Y capacitor value;

[0034] Figure 3 is a noise spectrum comparison diagram of the present application.

[0035] Wherein, 101a, first Y capacitor; 101b, second Y capacitor; 102a, first positive feedback resistor; 102b, second positive feedback resistor; 103, operational amplifier; 104, negative feedback capacitor; 105, negative feedback stabilization resistor; 106, first capacitor; 107, first resistor; 108, second capacitor; 109, second resistor. DETAILED DESCRIPTION

[0036] The related technologies in the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

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

[0038] The circuit of the embodiment utilizes weak positive feedback to regulate the voltage detection current injection type AEF of Y capacitor value, which comprises a Y capacitor value regulating circuit and an RC series branch. The Y capacitor value regulating circuit can regulate the Y capacitor value according to the adjustment of the positive feedback loop, so that the common mode filtering effect is equivalent to being increased without changing the volume, a low impedance loop is provided for common mode noise to suppress its conduction, and the adjustment and large flexibility are provided. The output of the operational amplifier is the inverse amplification of the noise voltage, which is connected to the positive and negative buses through the resistance and capacitance, and is converted into a current compensation signal to further suppress the EMI noise. The AEF is connected in parallel between the power supply input and the power electronic converter to form a common mode filter. The Y capacitor value regulating circuit comprises a capacitor resistance and an operational amplifier, the operational amplifier can amplify the noise voltage sampled at the midpoint to form a low impedance loop, so that the capacitor value is equivalent to being amplified, and the RC series branch circuit comprises a resistance and a capacitance, the capacitance impedance is small in the conduction noise frequency range, and the impedance after the series connection is mainly provided by the resistance.

[0039] The composition, main principle, use method and use effect of the application will be described in detail below with reference to the accompanying drawings of the embodiments of the application.

[0040] Embodiment

[0041] Reference Figure 1 The voltage detection current injection type AEF utilizing weak positive feedback to regulate Y capacitor value comprises:

[0042] The voltage detection current injection type AEF utilizing weak positive feedback to regulate Y capacitor value comprises a Y capacitor value regulating circuit and an RC series branch. The whole AEF is connected in parallel between the input power supply and the power electronic converter. The Y capacitor value regulating circuit comprises a capacitor resistance and an operational amplifier 103, wherein C Y is a capacitor to be amplified, which is a series connection of two Y capacitors with consistent values, i.e., a first Y capacitor 101a and a second Y capacitor 101b, and has three 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 bus lines of the noise source device. The adopted R a and R b are positive feedback loop resistors, i.e., a first positive feedback resistor 102a and a second positive feedback resistor 102b, which are used to adjust the capacitor value, and the negative feedback stabilizing resistor R F , i.e., the negative feedback stabilizing resistor 105, provides a loop for the input bias current and DC feedback of the operational amplifier, and the negative feedback capacitor C F , i.e., the negative feedback capacitor 104, is used to adjust the external equivalent impedance and R FIn parallel connection, within the conducted noise frequency range, the resistance is larger than the capacitance; therefore, the parallel connection of the two can be approximated as the capacitance. The non-inverting input of operational amplifier 103 is connected to ground with a positive feedback resistor R. a The output of operational amplifier 103 is connected to the positive feedback resistor R. b Connection. The inverting input of operational amplifier 103 is connected to the amplifier C. Y The capacitor is connected at its midpoint and connected to the output of operational amplifier 103 via the negative feedback capacitor C. F The connection is made between a capacitor and a negative feedback stabilizing resistor R. F Parallel connection. The Y capacitor capacitance adjustment circuit adjusts the capacitance C of the capacitor to be amplified. Y The midpoint voltage is sampled and amplified, causing the common-mode loop impedance to decrease proportionally after series connection, thus effectively becoming a capacitor with a larger capacitance. Therefore, the circuit can achieve precise adjustment of the capacitance value, obtaining greater common-mode insertion loss without changing the size, and providing better suppression of conducted common-mode noise. The output of operational amplifier 103 is connected to the common node of the RC series branch, which is a resistor R. S and capacitor C S The system consists of two series-resistive branches, one with a large capacitance value, used to isolate the bus voltage. Within the conducted noise range, the impedance of the series branches is primarily provided by the resistors. The two terminals of each branch are connected to the positive and negative bus of the power supply system, respectively. Compensation using the output voltage of the operational amplifier can improve the EMI filtering effect. (Close to C) Y The capacitor side is the input power supply port. The side closest to the RC series branch is the noise source device. According to... Figure 1 The circuit can be used to calculate the capacitance value after capacitor adjustment. 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 equation (1), where V out V is the output voltage of the operational amplifier. in This is the voltage at the inverting input terminal of the operational amplifier.

[0043]

[0044] The input current can be expressed based on the impedance between the input and output terminals of the operational amplifier, as shown in equation (2), where I in Z is the current flowing into the parallel network of the negative feedback resistor and capacitor. CF Z is the capacitance impedance between the inverting input and the output of the op-amp. CY The impedance of the capacitor to be amplified. The resistor R connected in parallel with the capacitor. F Compared to the capacitance impedance, it is relatively large within the range of conducted noise and can be ignored.

[0045]

[0046] Substitute (1) into (2), the external equivalent expression of the op-amp circuit can be calculated as shown in equation (3).

[0047]

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

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

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

[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 precisely controlled by the resistance values of the two positive feedback resistors R a and R b , which realizes the precise amplification of the capacitor C Y to be amplified, constructs a common-mode current low-impedance loop, and can effectively suppress common-mode electromagnetic interference noise conduction. The positive feedback effect needs to be weaker than the negative feedback branch to prevent the op-amp from self-oscillation. By utilizing the weak positive feedback effect, the filtering effect of the AEF circuit can be further adjusted.

[0055] Further analyzing the RC series branch, the input voltage of the inverting terminal of the op-amp can be calculated by voltage division using the equivalent impedance as shown in equation (7).

[0056]

[0057] The output voltage of the op-amp is the inverse amplification of the common-mode voltage of the bus. In the case of large capacitance amplification, the weak positive feedback coefficient can be controlled to make the capacitor C YThe absolute value of the impedance is slightly larger than the absolute value of the 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 after weak positive feedback regulation, so that the denominator is positive, and thus the output voltage of the operational amplifier is the common-mode noise voltage amplified in reverse, and at this time the denominator is smaller than the modulus, so that a larger amplification factor can be obtained, so as to convert the noise voltage into a large compensation current, thereby better suppressing EMI noise conduction. Weak positive feedback changes the equivalent impedance and provides a feedback voltage.

[0058] Figure 2 For a typical voltage detection current injection type AEF using weak positive feedback to regulate the capacitance value of Y capacitor, in this circuit diagram, L and C Y2 R is used for passive filtering, Y2 The common-mode inductance and the capacitance are small, so the volume is small, and it is mainly used to filter out high-frequency noise. The voltage detection current injection type AEF using weak positive feedback to regulate the capacitance value of Y capacitor is close to the noise source side, and the power electronic converter is an EMI noise source. The artificial power supply network is used to detect common-mode noise. In accordance with the impedance mismatch principle, in the case where the source impedance is large, the AEF is connected in parallel first and then the common-mode inductor is connected in series, so that the low-frequency electromagnetic interference suppression effect is better. By adjusting the capacitance value of the common-mode Y capacitor, a low-impedance loop can be constructed, and an inductor can be constructed to build a high-impedance loop to suppress the propagation of electromagnetic interference noise. On this basis, further compensation can be carried out to obtain better suppression effect.

[0059] Figure 3 For filtering effect comparison, that is, comparison effect of adopting the AEF of the application and bare noise. Figure 3 (a) is the circuit bare noise, Figure 3 (b) is the common-mode noise spectrum of the mixed EMI filter with the AEF, and it can be seen that the proposed AEF has a large suppression effect on common-mode electromagnetic interference noise.

[0060] Abbreviations in this embodiment

[0061] AEF Active EMI filter has active EMI filter

[0062] EMI Electromagnetic Interference electromagnetic interference

[0063] LISN Line Impedance Stabilization Network line impedance stabilization network

[0064] EUT Equipment Under Test equipment under test

[0065] To sum up, the application improves the problem that it is difficult to use large capacitance in the EMI filter, and effectively increases the common-mode EMI noise suppression capability while reducing the filter size by means of active equivalent increase of the capacitance compared with the traditional passive EMI filter; the application accurately adjusts the capacitance value, and the amplified capacitance has similar effect to the actual use of the same capacitance value, which can be adjusted according to the need, and the low-frequency band filtering effect is good. Therefore, the application can obtain larger common-mode capacitance without increasing the size, 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 is only the preferred embodiment of the application, not any form of limitation on the application, any simple modification of the above embodiment according to the technical essence of the application also belongs to the protection scope of the application, other equivalent changes and modifications still belong to the range of the technical scheme of the application.

Claims

1. A voltage-sensing current-injection type AEF that utilizes weak positive feedback to adjust the capacitance of a Y capacitor, characterized in that... include: Y capacitor capacitance adjustment circuit, RC series branch; The Y capacitor capacitance adjustment circuit amplifies the sampled noise voltage by introducing a positive feedback loop; The RC series branch converts the common-mode noise voltage into a compensation current, further suppressing the common-mode noise. The Y capacitor capacitance adjustment circuit includes: 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 terminal of the first Y capacitor (101a) and the second Y capacitor (101b) connected in series is connected to the inverting input terminal of the operational amplifier (103), and the two ends of the first Y capacitor (101a) and the second Y capacitor (101b) connected in series are respectively connected to the positive and negative busbars of the noise source device; the non-inverting input terminal 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 terminal and the output terminal of the operational amplifier (103) are respectively connected to the two ends of the second positive feedback resistor (102b); the inverting input terminal and the output terminal of the operational amplifier (103) are respectively connected to the two ends of the negative feedback capacitor (104) and the two ends of the negative feedback stabilizing 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: the first capacitor (106), the first resistor (107), the second capacitor (108), and the second resistor (109) are connected in series in sequence and their two ends are respectively connected to the positive and negative busbars of the noise source device; The common terminal of the first resistor (107) and the second capacitor (108) connected in series is connected to the output terminal of the operational amplifier (103).

2. The voltage detection current injection type AEF that utilizes weak positive feedback to adjust the capacitance of the Y capacitor according to claim 1, characterized in that, The first Y capacitor (101a) and the second Y capacitor (101b) each include a set of Y capacitors connected in series or in parallel.

3. The voltage detection current injection type AEF that utilizes weak positive feedback to adjust the capacitance of the Y capacitor according to claim 1, characterized in that, The capacitance values ​​of the first Y capacitor (101a) and the second Y capacitor (101b) are equal.

4. The voltage detection current injection type AEF that utilizes weak positive feedback to adjust the capacitance of the Y capacitor according to claim 1, characterized in that, The voltage-sensing current-injection type AEF is also connected to LISN and EUT respectively on both sides.

5. The voltage detection current injection type AEF that utilizes weak positive feedback to adjust the capacitance of the Y capacitor according to claim 1, characterized in that, The voltage-sensing current-injection type AEF has a positive feedback amplification factor of 1+R. b / R a At that time, the equivalent impedance of the op-amp 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) includes: （3） In equation (3), V in I represents the input voltage at the inverting input of the operational amplifier (103). in Z represents the current flowing through the negative feedback RC network. CF R represents the impedance of the negative feedback capacitor (104). a R b These represent the resistance values ​​of the first positive feedback resistor (102a) and the second positive feedback resistor (102b), respectively. When the first positive feedback resistor (102a) and the second positive feedback resistor (102b) connected to the operational amplifier (103) are adjusted, their equivalent common-mode impedance is determined by equation (6): （6） In equation (6), V CM I represents the common-mode noise voltage of the parallel connection point bus. CM C represents the current flowing through the Y capacitor. Y C represents the capacitance value of the Y capacitor. F represents the capacitance value of the negative feedback capacitor (104), and s represents the complex frequency variable.

6. The voltage detection current injection type AEF that utilizes weak positive feedback to adjust the capacitance of the Y capacitor according to claim 1, characterized in that, The negative feedback capacitor (104) is composed of multiple capacitors connected in parallel.

7. The voltage detection current injection type AEF that utilizes weak positive feedback to adjust the capacitance of the Y capacitor according to claim 1, characterized in that, The relationship between the output voltage of the operational amplifier (103) and the common-mode noise voltage includes: （7） In equation (7), V out This represents the output voltage of the operational amplifier (103).

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