Isolated active EMI filter without adding elements to power lines

Abstract

To provide an isolated active EMI filter with no additional elements on the power line, in which active circuit elements are isolated from the power line, and a method for reducing EMI noise using the same.SOLUTION: An isolated active EMI filter 100 is an EMI filter for preventing noise emitted from a power line cable, and does not have any elements added to the power line. The isolated active EMI filter 100 includes a common mode choke 110 arranged on the power supply side, a Y capacitor 120 arranged on the EMI source side, a detection winding 130 that detects the noise current flowing through the common mode choke 110, an amplifier 140 that amplifies the noise current, and a transformer 150 that injects a signal from the secondary coil into the Y capacitor as a compensation signal.SELECTED DRAWING: Figure 1

Description

[Technical Field] 【0001】 The present invention relates to an EMI filter, and more particularly to an isolated active EMI filter that does not involve the addition of elements to power lines. [Background technology] 【0002】 Most consumer electronics and industrial electrical systems will be fitted with EMI filters to prevent conducted EMI noise emitted through power line cables. 【0003】 To prevent common-mode conducted noise, a filter consisting of a common-mode choke and a Y-capacitor is typically used. In high-power, high-current electrical systems, the noise reduction performance is reduced due to the magnetic saturation phenomenon of the common-mode choke. To obtain sufficient attenuation performance to prevent this, it is necessary to use a multi-stage filter or an expensive, high-performance choke, which significantly increases the size and cost of the EMI filter. Therefore, there are attempts to use active EMI filters that can overcome the limitations of passive EMI filters and effectively improve performance, and it is preferable that active EMI filters do not require chokes to be added to the power lines. 【0004】 Active EMI filters have a feedback circuit structure that senses noise voltage and current using capacitors and transformers, and then applies compensation voltage and current back to the transformers and capacitors to cancel them out. However, when a transformer is added to the power line in an active EMI filter to detect and compensate for noise, the performance of high-power, high-current electrical systems deteriorates significantly due to the magnetic saturation of the transformer. In other words, conventional active EMI filters that do not have a transformer added to the power line have been designed to detect and compensate for noise via a capacitor. 【0005】 However, in active EMI filters, connecting capacitors to power lines for noise detection and compensation results in the active circuit elements no longer being isolated from the power lines, significantly reducing reliability and stability against electrical overload (EOS). In other words, an active EMI filter needs a structure that isolates the active circuit elements from the power lines without adding chokes to them. [Overview of the project] [Problems that the invention aims to solve] 【0006】 The problem that this invention aims to solve is to provide an isolated active EMI filter that does not require the addition of elements to the power line, in which the active circuit elements are isolated from the power line without adding any elements to the power line. 【0007】 Another problem that the present invention aims to solve is to provide an EMI noise reduction method using an isolated active EMI filter that does not require the addition of elements to the power line, in which the active circuit elements are isolated from the power line without adding any elements to the power line. [Means for solving the problem] 【0008】 An isolated active EMI filter according to a first embodiment of the present invention, which does not involve adding elements to a power line, is provided to achieve the above objectives and comprises: a common mode (CM) choke located on the power supply side to which power is supplied, on which a live line and a neutral line connected to an EMI source are each wound; a Y capacitor located on the EMI source side that generates EMI, consisting of two capacitors connected in series, the two capacitors connected in parallel between the live line and the neutral line and commonly connected to ground; a detection winding wound in a coil over the common mode choke to detect the noise current of the common mode choke; an amplification unit that amplifies the noise current detected by the detection winding; and a transformer provided in front of the Y capacitor, on which the primary coil receives the signal amplified by the amplification unit, the secondary coil is connected to ground connected to the Y capacitor and isolated from the power line, and the signal from the secondary coil is injected into the Y capacitor as a compensation signal. 【0009】 An isolated active EMI filter without adding any elements to a power line according to a second embodiment of the present invention for achieving the above objectives comprises: a common mode (CM) choke arranged on the power supply side to which power is supplied, on which a live line and a neutral line connected to an EMI source are each wound by a winding; a Y capacitor arranged on the EMI source side that generates EMI, consisting of two capacitors connected in series, the two capacitors connected in parallel between the live line and the neutral line and commonly connected to ground; a transformer section provided upstream of the Y capacitor, on which a primary coil senses the noise voltage of the Y capacitor and transforms it via a secondary coil, and which is isolated from the power line; an amplifier section that amplifies the noise voltage detected and transformed by the transformer section; and a compensation winding that is wound in a coil over the common mode choke and injects the noise signal amplified by the amplifier section into the common mode choke. 【0010】 An isolated active EMI filter without adding elements to a power line according to a third embodiment of the present invention for achieving the above objectives comprises: a common mode (CM) choke arranged on the EMI source side that generates EMI, with a live line and a neutral line connected to the EMI source each wound around a winding; a Y capacitor arranged on the power supply side that receives power, consisting of two capacitors connected in series, the two capacitors connected in parallel between the live line and the neutral line and commonly connected to ground; a detection winding wound in a coil over the common mode choke to detect the noise current of the common mode choke; an amplification unit that amplifies the noise current detected by the detection winding; and a transformer provided in front of the Y capacitor, the primary coil receiving the signal amplified by the amplification unit, the secondary coil connected to ground connected to the Y capacitor and isolated from the power line, and the transformed signal via the secondary coil being injected into the Y capacitor as a compensation signal. 【0011】 An isolated active EMI filter according to a fourth embodiment of the present invention, which does not involve adding elements to a power line, is provided to achieve the above objectives. This isolated active EMI filter comprises: a common mode (CM) choke arranged on the EMI source side that generates the EMI, with a live line and a neutral line connected to the EMI source each wound around it; a Y capacitor arranged on the power supply side that receives power, consisting of two capacitors connected in series, the two capacitors connected in parallel between the live line and the neutral line and commonly connected to ground; a transformer provided upstream of the Y capacitor, with a primary coil that senses the noise voltage of the Y capacitor and transforms it via a secondary coil, and is isolated from the power line; an amplification unit that amplifies the noise voltage transformed by the transformer; and a compensation winding that is wound around the common mode choke in a coil and injects the noise signal amplified by the amplification unit into the common mode choke as a compensation signal. 【0012】 A first embodiment of the present invention for achieving the aforementioned other objectives, which provides an EMI noise reduction method using an isolated active EMI filter without adding any elements to a power line, includes a passive EMI filter comprising: a common-mode (CM) choke located on the power supply side to which power is supplied, with a live line and a neutral line connected to an EMI source each wound around a winding; and a Y capacitor located on the EMI source side that generates EMI, consisting of two capacitors connected in series, the two capacitors connected in parallel between the live line and the neutral line and commonly connected to ground. The method includes adding an active element to the passive EMI filter to reduce EMI noise, and further includes the steps of: detecting the noise current of the common-mode choke via a detection winding formed by winding a coil around the common-mode choke; amplifying the noise current detected by the detection winding; and transforming the amplified signal received via the primary coil of a transformer located upstream of the Y capacitor via a secondary coil and injecting it into the Y capacitor, wherein the secondary coil of the transformer is connected to ground connected to the Y capacitor and isolated from the power line. 【0013】 A second embodiment of the present invention, which aims to achieve the aforementioned other objectives, provides an EMI noise reduction method using an isolated active EMI filter without adding elements to a power line, which is placed on the power supply side to which power is supplied, and connects to the EMI source, a live line and a neutral line. A method for reducing EMI noise by adding an active element to a passive EMI filter comprising a common mode (CM) choke, each of which is wound with a winding, and a Y capacitor, which is located on the EMI source side that generates EMI and consists of two capacitors connected in series, the two capacitors being connected in parallel between the live line and the neutral line and commonly connected to ground, wherein the method includes the steps of: the primary coil of a transformer provided in front of the Y capacitor senses the noise voltage using the Y capacitor as a detection capacitor and transforming it via the secondary coil of the transformer; amplifying the noise voltage transformed via the secondary coil; and injecting the amplified noise signal into the common mode choke via a compensation winding that is wound in supination around the common mode choke, and wherein the secondary coil of the transformer is connected to ground connected to the Y capacitor and isolated from the power lines. 【0014】 A third embodiment of the present invention for achieving the aforementioned other objectives, which provides an EMI noise reduction method using an isolated active EMI filter without adding any elements to a power line, includes a passive EMI filter comprising: a common mode (CM) choke located on the EMI source side that generates the EMI, with a live line and a neutral line connected to the EMI source each wound around a winding; and a Y capacitor located on the power supply side that receives power, consisting of two capacitors connected in series, the two capacitors connected in parallel between the live line and the neutral line and commonly connected to ground. The method includes adding an active element to the passive EMI filter to reduce EMI noise, and further includes the steps of: detecting the noise current of the common mode choke via a detection winding formed by winding a coil around the common mode choke; amplifying the noise current detected by the detection winding; and transforming the amplified signal, which is input via the primary coil of a transformer located upstream of the Y capacitor, via the secondary coil of the transformer and injecting it as a compensation signal into the Y capacitor, wherein the secondary coil of the transformer is connected to ground connected to the Y capacitor and isolated from the power line. 【0015】 A fourth embodiment of the present invention for achieving the aforementioned other objectives, which provides an EMI noise reduction method using an isolated active EMI filter without adding any elements to a power line, is a method for reducing EMI noise by adding an active element to a passive EMI filter comprising: a common mode (CM) choke located on the EMI source side that generates the EMI, with a live line and a neutral line connected to the EMI source each wound around a winding; and a Y capacitor located on the power supply side that is supplied with power, consisting of two capacitors connected in series, the two capacitors connected in parallel between the live line and the neutral line and commonly connected to ground, wherein the passive EMI filter is equipped with an active element, and the method includes the steps of: the primary coil of a transformer provided in front of the Y capacitor senses the noise voltage of the Y capacitor and transforms it via a secondary coil; amplifying the transformed noise voltage; and injecting the amplified noise signal as a compensation signal into the common mode choke via a compensation winding that is wound in superimposed on the common mode choke, and the secondary coil of the transformer is isolated from the power line by being connected to ground connected to the Y capacitor. [Effects of the Invention] 【0016】 In most home appliances and industrial electrical and electronic equipment, EMI filters must be installed to prevent conducted EMI noise emitted through power line cables. However, according to the present invention, an isolated active EMI filter that does not require the addition of elements to the power line, and an EMI noise reduction method using the same, the same noise attenuation performance can be obtained with a smaller size and lower cost than when using only a passive filter. 【0017】 Furthermore, according to the present invention, when a multi-stage passive EMI filter is conventionally used to achieve sufficient noise attenuation, adding an isolated active EMI filter according to the present invention, which does not require additional elements on the power line, can reduce the number of filter stages, thereby reducing the size and cost of most electrical and electronic equipment. [Brief explanation of the drawing] 【0018】 [Figure 1] This is a circuit diagram showing the configuration of a first embodiment of an isolated active EMI filter according to the present invention, which does not involve adding elements to the power line. [Figure 2] This figure shows an example of an AEF configuration according to the present invention, and is a proposed isolation AEF configuration for a transformer that is provided in addition to (add-on to) a CM LC EMI filter. [Figure 3] This figure shows a circuit model of an AEF according to one embodiment of the present invention. [Figure 4] This diagram shows the equivalent circuit of half the circuit, including parasitic components. [Figure 5] This figure shows the equivalent circuit model of a CM choke in a power line, including the influence of the detection winding. [Figure 6A] This figure shows the changes in the current path and the capacitor effect (CY,eff(s)) of the Y capacitor due to the active EMI filter in each frequency domain. [Figure 6B] Same as above. [Figure 6C] Same as above. [Figure 7A] This figure shows the power line impedance (Z-line) curve when viewed from the position of the Y capacitor toward the power supply side, and represents the case when Nsen does not satisfy equation 19. [Figure 7B] This figure shows the power line impedance (Z-line) curve when viewed from the position of the Y capacitor toward the power supply side, and shows the cases when Nsen satisfies equation 19. [Figure 8A] This figure compares loop gains, showing the loop gains in an unstable situation without damping components Rd1, Cd, Rd2 and phase compensators Rc, Cc. [Figure 8B] This figure compares the loop gains, showing the loop gains of the aforementioned components under stable conditions. [Figure 9] This is a circuit diagram showing a second embodiment of an isolated active EMI filter according to the present invention, which does not involve adding elements to the power line. [Figure 10] This is a circuit diagram showing a third embodiment of an isolated active EMI filter according to the present invention, which does not involve adding elements to the power line. [Figure 11] This is a circuit diagram showing a fourth embodiment of an isolated active EMI filter according to the present invention, which does not involve adding elements to the power line. [Figure 12] This flowchart shows a method for reducing EMI noise by adding an active element to a passive EMI filter, corresponding to a first embodiment of an isolated active EMI filter without adding elements to the power line according to the present invention. [Figure 13] This flowchart shows a method for reducing EMI noise by adding an active element to a passive EMI filter, corresponding to a second embodiment of an isolated active EMI filter without adding elements to the power line according to the present invention. [Figure 14] This flowchart shows a method for reducing EMI noise by adding an active element to a passive EMI filter, corresponding to a third embodiment of an isolated active EMI filter without adding elements to the power line according to the present invention. [Figure 15] This flowchart shows a method for reducing EMI noise by adding an active element to a passive EMI filter, corresponding to a fourth embodiment of an isolated active EMI filter without adding elements to the power line according to the present invention. [Modes for carrying out the invention] 【0019】 The present invention relates to an isolated active EMI filter that does not require the addition of elements to a power line and a method for reducing EMI noise using the same. The isolated active EMI filter is located on the power supply side to which power is supplied and comprises a common mode (CM) choke, a Y capacitor, a detection winding wound around the common mode choke in a coil to detect the noise current of the common mode choke, an amplification unit that amplifies the noise current detected by the detection winding, and a transformer provided before the Y capacitor, the primary coil receiving the signal amplified by the amplification unit, the secondary coil being connected to ground connected to the Y capacitor and isolated from the power line, and the transformer injecting the signal from the secondary coil into the Y capacitor as a compensation signal. 【0020】 Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. The embodiments and configurations shown in the drawings described herein are merely preferred embodiments of the present invention and do not represent the entirety of the technical concept of the present invention. It should be understood that there are various equivalents and modifications that can be substituted for these at the time of filing this application. 【0021】 Figure 1 is a circuit diagram showing the configuration of a first embodiment of an isolated active EMI filter according to the present invention, which does not involve adding elements to the power line. The first embodiment of the present invention comprises a passive EMI filter consisting of a common-mode (CM) choke 110 and a Y capacitor 120, and an EMI filter 100 consisting of a detection winding 130, an amplification unit 140, and a transformer 150. 【0022】 The common-mode (CM) choke 110 is located on the power supply side, and has windings for the live line and neutral line, which are connected to the EMI source. 【0023】 The Y capacitor 120 is located on the EMI source side that generates EMI, and consists of two capacitors connected in series. These two capacitors are connected in parallel between the live line L and the neutral line N, and are also connected to ground. 【0024】 The detection winding 130 is wound around the common mode choke 110 with a coil, and detects the noise current flowing through the common mode choke 110. The number of turns (N sen ) of the detection winding 130 is such that when the capacitance of the parasitic circuit of the common mode (CM) choke 110 is C cm and the capacitance of the parasitic circuit of the detection winding 130 is C sen , it is preferably smaller than the square root of 2C cm / C sen . 【0025】 The amplification unit 140 amplifies the noise current detected via the detection winding 130. 【0026】 The transformer 150 is provided in front of the Y capacitor 120. The primary coil receives the signal amplified by the amplification unit, and the secondary coil is connected to the ground connected to the Y capacitor 120 and is isolated from the power line, and injects the signal of the secondary coil into the Y capacitor 120 as a compensation signal. 【0027】 FIG. 2 is an example of the AEF configuration according to the present invention, and shows an insulated AEF configuration of a proposed transformer additionally provided in the CM L-C EMI filter. FIG. 3 is a diagram showing a circuit model of the AEF according to an embodiment of the present invention. 【0028】 The insulated active EMI filter without adding an element to the power line according to the present invention may further include a low pass filter (Low pass filter) in order to solve the stability problem caused by the resonance of the detection winding in the high frequency range. (See FIG. 3) The low pass filter includes a resistor R f and a capacitor C f . 【0029】 One end of the resistor R f is connected to the detection winding, and the other end is connected to the + input terminal of the amplification unit. One end of the capacitor C f is connected to the resistor R fA capacitor C is connected to the other end of the amplifier and the + input terminal of the amplifier, with the other end connected to ground. f It is equipped with and located at the input terminal of the amplification section. 【0030】 Furthermore, the impedance (Z) viewed from the input terminal of the amplification unit 140 toward the low-pass filter side. in,AEF ) is the parasitic RC component impedance (Z) of the detected winding 130 in the frequency range of interest. sen,para It is preferable to set it higher than ). 【0031】 JPEG0007875639000001.jpg42170 【0032】 Furthermore, the isolated active EMI filter according to the present invention, which does not involve adding elements to the power line, may further include a bypass branch to avoid the resonance of the transformer, providing stability as a bypass and damping circuit, and mitigating performance degradation due to resonance between the EMI source impedance and the Y capacitor. (See Figure 3) The bypass branch is a first resistor R d1 , capacitor C d and the second resistor R d2 It may be provided. 【0033】 1st resistance R d1 One end of the Y capacitor is connected to the Y capacitor, and the other end is connected to the secondary coil of the transformer, and the capacitor C d One end of the second resistor R is connected to the other end of the resistor. d2 One end of the cable is connected in series with the other end of the capacitor, and the other end is connected to ground. 【0034】 Furthermore, the isolated active EMI filter according to the present invention, which does not involve adding elements to the power line, may further include a phase compensator for stability in the low-frequency range. (See Figure 3) 【0035】 The phase compensator comprises a resistor Rc and a capacitor Cc connected in parallel. One end of the parallel-connected resistor Rc and capacitor Cc is connected to the negative input terminal of the amplifier, and the other end of the parallel-connected resistor Rc and capacitor Cc is connected in parallel to the output terminal of the amplifier. 【0036】 This invention proposes a novel structure for a fully-transformer-isolated AEF. Referring to Figure 2, an AEF according to one embodiment of the present invention is added as an add-on to a conventional CM LC EMI filter consisting of a CM choke and a Y capacitor. The AEF structure according to one embodiment of the present invention is similar to the conventional CSCC AEF topology, but an injection transformer is added between the output of the amplification section and the compensating Y capacitor. Because the injection transformer is not located on the main power line, only a small compensation signal current flows through the transformer. The injection transformer can be compactly implemented because the current is small regardless of the application's operating current, and the risk of magnetic saturation and thermal problems is low. In addition, an additional transformer is not required for the sensing section of the AEF, although a thin noise detection wire is further wound around the conventional commercial CM choke. Attempts have been made to directly add sensing windings on top of commercial CM chokes, but the adverse effects of the sensing windings and the maximum allowable number of turns have not been investigated. In summary, the main novel feature of the AEF according to one embodiment of the present invention is that it allows for fully transformer-isolated and compact-sized design without adding any additional components to the main power line. Thanks to these characteristics, the AEF according to the present invention is smaller in size and has superior performance compared to other CSVC AEFs for transformer isolation. 【0037】 This invention provides numerous useful explicit design guidelines for the complete design of an AEF according to one embodiment of the present invention. As described later, the noise attenuation performance is evaluated by analyzing the isolation AEF of the transformer, and appropriate design guidelines for the performance and stability of the AEF are provided based on the analysis. The insertion loss and loop gain of the AEF filter are measured and verified using a vector network analyzer (VNA). The reduction of CM CE noise by the AEF is also evident in actual product SMPS boards. In addition, the amount of leakage current to ground is measured to confirm the safety of using the AEF. 【0038】 The following analyzes an AEF according to one embodiment of the present invention. Referring to Figure 3, CY represents the capacitance of the Y capacitor. The CM choke is L cm and M cm This is modeled as follows, which shows the self-inductance and mutual inductance of windings on a power line. 【0039】 The AEF (Automatically Electron Emission Circuit) primarily consists of a sensing winding wound around a CM choke, an amplification section, and an injection transformer. The winding ratio between the power line winding and the sensing winding is 1:N. sen The detection winding's own inductance is set to approximately N sen 2 L cm It is given as M sen This shows the mutual inductance between the power line winding and the AEF input detection winding. Similarly, M inj This indicates the mutual inductance of the injection transformer, and the winding ratio of the primary winding to the secondary winding is 1:N inj The following settings are used. The self-inductance on each surface is L inj and N inj 2 L inj It is given as M cm M sen and M inj These are k cm L cm , k sen N sen L cm and kinj N inj L inj This is calculated as follows: Here, k cm , k sen and k inj The coefficients of each bond are shown. cm , k sen and k inj The value of R is generally between 0.99 and 1 in actual designs. The amplification section is implemented in a non-inverting operational amplifier configuration with resistors R1 and R2. 【0040】 Considering the feedback stability of the AEF, several additional components such as a low-pass filter, bypass branch, and phase compensator are required, as shown in Figure 3. f and C f To solve the stability problem caused by resonance in the detection winding in the high-frequency range, a low-pass filter is configured using an operational amplifier. d1 , C d and R d2 It operates for stability as a bypass and damping circuit to avoid resonance in the injection transformer, and additionally mitigates performance degradation due to resonance between the impedance of the noise source and the Y capacitor. c and C c This is a phase compensator for stability in the low frequency range. 【0041】 Even if the AEF's ground reference voltage is set to be different from ground, the AEF is symmetric with respect to the AC zero potential, and the circuit can be analyzed by dividing it into two parts. Figure 4 shows the equivalent circuit of the half portion including parasitic components. Referring to Figure 4, for more accurate representation, the parasitic circuit parameters of the CM choke, sensing winding, and injection transformer are also modeled, and R cm , C cm , R sen , C sen , R inj1 , C inj1 , R inj2 and C inj2These are included in each. The CM noise sources of the Equipment Under Test (EUT) are the Thevenin equivalent circuit V n and Z n It is modeled as follows, showing the CM noise source voltage and impedance. LISN This indicates the impedance of the line impedance stabilization network (LISM). line , Z in,AEF and Z Y,eff These represent the impedances viewed in each direction, relative to the AC zero potential. 【0042】 The operating principle of the AEF is analyzed based on the expressions for the effective inductance of the CM choke and the effective capacitance of the Y capacitor 120 branch. The effective inductance of the CM choke is explained. 【0043】 The impedance viewed from in front of the CM choke toward the power line is given by Kirchhoff's law as follows: 【number】 Here, 【number】 【number】 【number】 【number】 L cm,eff The effective inductance of the CM choke is shown, where the inductance cancellation term X(s) is given. X(s) is (2M sen I sen ) / (L cm I cm ) defined, where I cm and I sen In Figure 4, (L cm +M cm ) and 2Nsen 2 L cm Each shows the current flowing through the inductance branch of L. Z sen,para represents the parasitic RC component impedance of the detection winding. Z in,AEF represents the impedance seen from the input terminal of the amplifier section toward the low-pass filter side. The input impedance of the operational amplifier is assumed to be large within the frequency range of interest and is ignored in Equation 5 (Equation 5). 【0044】 FIG. 5 is a diagram showing a CM choke equivalent circuit model in a power supply line including the influence of the detection winding. The influence of the detection winding on the CM choke inductance is summarized and shown in FIG. 5. Referring to FIG. 5, the box on the right shows 2M sen shows a CM choke equivalent circuit model in a power supply line considering the voltage induced by 2sM sen I sen The induced voltage of is of the opposite polarity to the voltage drop of s(L cm +M cm )I cm Defining X(s) as (2M sen I sen ) / (L cm I cm ), the total voltage of the choke inductance can be simplified to s(1 + k cm- X(s))L cm I cm . Therefore, the effective inductance L cm,eff of the CM choke is expressed as (1 + k cm- X(s))L cm as given by Equation 2 (Equation 2). 【0045】 When there is no detection winding, k sen = X(s) = 0, and thus L cm,eff is simply given by (1 + k cm )L cm . However, in Equation 3 (Equation 3), sN sen 2 L cm is (Z in,AEF ||Z sen,paraWhen it is much higher than ), k cm and k sen Since it approaches 1, X(s) ≈ 2k sen 2 And then, L cm,eff ≒L cm (1+k cm- -2k sen 2 This means that the choke inductance can be critically affected by the current flowing through the sensing winding. Therefore, in order to maintain the choke inductance, the number of turns of the sensing winding must be N. sen It must be restricted. 【0046】 Next, we will explain the effective capacitance of the Y capacitor. Y capacitor branch Z Y,eff The impedance viewed in the direction of can be expressed by equations 6 to 11. 【number】 Here, 【number】 【number】 【number】 【number】 【number】 【0047】 Here, α(s) and β(s) can be understood physically as a boosting factor and a bypass factor, respectively, as will be described later. G1(S) is V in From V in,amp This is the voltage gain up to G amp (s) is V in,amp From V out,ampThis is the gain of the amplification section up to [value]. We assume that the frequency bandwidth of the operational amplifier is sufficiently higher than the frequency range of interest. Z in Equation 6 (Equation 6) Y,eff The expression is effective capacitance C Y,eff It can be understood as the impedance of (s) and is defined as shown in equation 12 (equation 12). 【number】 【0048】 Figures 6A, 6B, and 6C show the change in C when the frequency is changed. Y,eff The figures show the change in (s), Figure 6A shows the AEF operation over the frequency range, Figure 6B shows the plots of α(s) and β(s), and Figure 6C shows Z Y,eff The impedance curves for each are shown below. 【0049】 C by changing the frequency Y,eff The changes in (s) are summarized in Figures 6A, 6B, and 6C. The effect of AEF and the change in the current path in the Y capacitor branch are explained in Figure 6A. The dotted box is C Y,eff· This shows the effect of AEF on f. op,min and f op,max These are the minimum and maximum target operating frequencies of the AEF that can be designed using the AEF's circuit parameters, respectively. 【0050】 For example, the magnitudes of α(s) and β(s) of a properly designed AEF are shown in Figure 6B according to frequency. The impedance Z of the Y capacitor branch. Y,eff This is also depicted in Figure 6C. op,min At sufficiently low frequencies, both α(s) and β(s) are much smaller than 1, and Z in equation 6 (equation 6) Y,eff It can be easily expressed as 1 / sC. Y This approximates f. This means that the bypass circuit and injection transformer are negligible compared to the impedance of CY, and the noise voltage compensated from AEF is also very small. op,min from f op,maxIn the AEF operating frequency range up to -αV, α(s) is greater than 1, but β(s) is much smaller than 1. That is, the AEF is -αV in Figure 6A. in As shown, it provides a compensation voltage to the Y capacitor branch, while the bypass circuit is negligible. 【0051】 The magnitude of α(s) is the product of the voltage gains of the detection winding, amplification section, and injection transformer N over the operating frequency range. sen N inj It is mainly maintained by (1+R2 / R1). Therefore, the CM current flowing through the Y capacitor branch is (1+N sen N inj (1+R2 / R1)) amplifies the effective capacitance as shown in Figure 6C (1+N sen N inj (1+R2 / R1))C Y It increases to the frequency f op,max As it increases, α(s) begins to decrease, indicating that the compensation voltage from the AEF decreases. At the same time, β(s) approximates 1, which is the impedance of the bypass branch (R d2 +1 / sC d This means that the impedance is lower than the impedance of the injection transformer path. Therefore, the CM noise current flows mainly through the bypass branch, Z Y,eff The impedance is (1 / sC) Y +2(R d2 +1 / sC d It approximates )). 【0052】 Figure 6C shows f op,max C in the following frequency range d and R d2 Because Z is added to the current path, Y,eff The size is 1 / sC Y This indicates that it will be significantly larger than the magnitude of the damping resistor R. d2 This plays a crucial role in mitigating resonance between the Y capacitor and the CM noise source impedance. In many cases, resonance significantly degrades the performance of the entire CM filter, so it is necessary to avoid it. 【0053】 Next, we will explain the insertion loss of the entire filter. The noise attenuation performance of a filter is generally quantified as the insertion loss (IL), which is defined as the ratio of the noise voltage received by the LISN without the filter to the noise voltage of the LISN with the filter installed. In Figure 4, the IL of the entire EMI filter is derived as shown in Equation 13. JPEG0007875639000014.jpg34170 【0054】 JPEG0007875639000015.jpg54170 【0055】 Next, we will describe the design guidelines for the AEF provided in this invention. We will develop practical design guidelines for the AEF considering performance and stability. First, we will describe the design of the detection winding and the input low-pass filter. 【0056】 The detection winding is wound directly onto the CM choke, and no additional detection transformer is required. It is preferable to avoid using a separate detection transformer from a size and cost perspective. However, as mentioned above, the CM choke inductance L cm,eff and power line impedance Z line This can be reduced by an additional detection winding. The AEF according to the present invention is a Y capacitor C Y,eff Even if we successfully increase it, the reduced power line impedance Z line This may reduce the noise attenuation performance of all CM EMI filters. Therefore, Z line To prevent a decrease in performance, appropriate design guidelines for detection windings are necessary. 【0057】 JPEG0007875639000016.jpg92170JPEG0007875639000017.jpg30170 【0058】 Easier, R f and C f These are selected so that they result in equations 15 (equation 15) and 16 (equation 16). JPEG0007875639000018.jpg29170JPEG0007875639000019.jpg27170 【0059】 If the inequality condition in equation 14 (equation 14) is sufficiently satisfied, then (Z in,AEF ||Z sen,para )≒Z sen,para Therefore, sN sen 2 L cm (Z in,AEF ||Z sen,para The frequency point at which it begins to become larger than ) is N sen 2 L cm and C sen The resonant frequency between these two points is approximated by equation 17 (equation 17). JPEG0007875639000020.jpg29170 【0060】 Secondly, f r,sen As in equation 18 (equation 18), f r,cm It must be higher, The design guidelines for the number of turns of the detection winding are extracted as shown in Equation 19 (Equation 19). JPEG0007875639000022.jpg33170 【0061】 Here, L cm,eff is, (1+k cm )L cm ≒L cm It approximates the maintained Z. line The design guidelines in Equation 19 (Equation 19) that guarantee this are derived from the maximum allowable winding ratio of the detection winding. Equation 19 (Equation 19) for CM choke and C cm , C sen Although the exact value of the parasitic capacitance is unknown before design, Equation 19 (Equation 19) can still provide a useful guideline for the number of turns of the winding. 【0062】 Figures 7A and 7B show the power line impedance (Z) when viewed from the position of the Y capacitor toward the power supply side. line Figure 7A shows the curve of N sen When equation 19 (equation 19) is not satisfied, Figure 7B shows N sen The cases where equation 19 (equation 19) is satisfied are shown. An example of the numerical values ​​is shown in Figure 7. N sen The two different values ​​of C are for a simple analysis. cm and C sen Tested with AEF designed with the same fixed value. Z with and without AEF line The size, that is, Z line W / O,AEF and Z line W / ,AEF These are being compared. In Figure 7A, formula 19 (equation 19) is N sen =2 is not satisfied, f r,sen is f r,cm It is lower. Conversely, in Figure 7B, equation 19 (equation 19) is N sen It satisfies =0.5, f r,sen is f r,cm Higher. Consequently, in Figure 7A, Z line W / AEF is, Z line W / O,AEF While it decreased significantly compared to, in Figure 7B, Z line W / AEF It remains almost unchanged. 【0063】 Furthermore, using AEF, Z in the high-frequency range line It was found that another resonance occurs. The resonance occurs at the frequency shown in Figures 7A and 7B. The resonance is detected in JPEG0007875639000023.jpg14170 and is caused by the winding. This resonance negatively affects system feedback stability in the high-frequency range, so to suppress the resonance, an R is added to the input terminal of the operational amplifier. f and C f A low-pass filter consisting of the following is required. For a low-pass filter that does not affect AEF performance in the operating frequency range, the cutoff frequency of the filter is the maximum operating frequency f. op,max It must be greater than [the specified value], but less than the resonant frequency of equation 20 (equation 20). JPEG0007875639000024.jpg30170 【0064】 Equations 15, 16, and 20 can serve as guidelines for low-pass filter design. 【0065】 Next, we will describe the design of the injection transformer and the amplifier section. The design of the injection transformer and amplification elements is primarily based on the main performance parameters of the AEF shown in Figure 6, f op,min ,f op,max and C Y,eff Determine the capacitor C at the output of the amplification section. o This is used to block unwanted signals at frequencies lower than the target operating frequency range. inj A C connected in series with it o This constitutes a high-frequency filter, and its cutoff frequency is derived as shown in Equation 21 (Equation 21), which determines the minimum operating frequency of the AEF. JPEG0007875639000025.jpg31170 【0066】 f op,min L at frequency inj A C connected in series with it o The impedance decreases sharply, increasing the output current of the operational amplifier. Therefore, R o To limit the impedance at the resonant frequency, it is added to the output of the op-amp, but sL across the entire operating frequency range. inj It must be significantly smaller than that. 【0067】 On the other hand, as explained in Figure 6A, the maximum operating frequency f of the AEF is determined by the frequency boundary at which the impedance of the bypass branch becomes lower than the impedance of the injection transformer path. op,max This is determined. Similar to the resonance due to the detection winding shown in Figure 7, the resonance of the secondary winding of the injection transformer can cause feedback instability, so the bypass branch must start operating at a frequency lower than the resonant frequency. The resonance of the secondary winding is given by f as in Equation 22 (Equation 22). op,max higher frequency This occurs with JPEG0007875639000026.jpg14170. JPEG0007875639000027.jpg30170 【0068】 f op,max This is the inductance part (1-k) of the injection transformer. inj 2 )N inj 2 L inj and the capacitance C of the bypass branch d The resonance between them determines the result as shown in equation 23 (equation 23). JPEG0007875639000028.jpg29170 【0069】 Substituting equation 23 (equation 23) into equation 22 (equation 22), C d and C inj 2 The relationships are extracted as follows: JPEG0007875639000029.jpg23170 【0070】 A small damping resistance R d1 and R d2 This is necessary for stability at high frequencies. A R of several tens of ohms. d2 This is recommended to mitigate resonance between the Y capacitor and the CM noise source's pedance in the high-frequency range, which will be demonstrated experimentally in Chapter IV. 【0071】 Except for the resonance point, AEF operation with resistor R d1 , R d2 and R inj 2 Assuming that the influence of is negligible, the condition of equation 24 (equation 24) is that equations 7 (equation 7) to 11 (equation 11) are f op,max It can be approximated as shown in Equation 25 (Equation 25) within the frequency range up to [a certain point]. JPEG0007875639000030.jpg22170 【0072】 In equation 12 (equation 12), Y is a capacitor and C is an effective capacitance. Y,eff (s) can be simplified to equation 26 (equation 26). JPEG0007875639000031.jpg24170 【0073】 G amp (s) Phase compensation element R c and C c This should have little effect on the AEF operation, and equation 26 (equation 26) is further simplified to a frequency-independent value as shown in Figure 6. JPEG0007875639000032.jpg23170 【0074】 Finally, some useful design guidelines for AEF can be derived as follows: Even if N sen Even if it is restricted by equation 19, in equation 27, C Y,eff is, N inj And by increasing the gain of the amplification section (1+R2 / R1), C Y It can be designed to be multiple times N. inj As increases, the maximum operating frequency f op,max It decreases according to equation 23 (equation 23). Also, a high amplifier gain requires a large output voltage swing and a large gain bandwidth for the operational amplifier. Therefore, N inj The appropriate values ​​for (1+R2 / R1) are the cost of the OP-amp and the f of the AEF. op,max The selection must be made with these factors in mind. 【0075】 Furthermore, the condition for equation 22 (equation 22) is the f of AEF. op,max is the N of the injection transformer inj , L inj and C inj 2 This means that it can be adjusted by the parasitic capacitance C. inj2 Since N is not an independent design parameter, inj and L inj is high f op,maxTo achieve this, it must be designed to be small. However, small N inj is C Y,eff Make it smaller, L inj Lowering it leads to f from equation 21 (equation 21). op,min To improve this. Consequently, we propose the following design process for optimized AEF performance. First, C o It is designed to be as large as possible within a given physical package size, L inj The target is f op,min Therefore, it decreases to the limit of equation 21 (equation 21). Secondly, the maximum C Y,eff To achieve N inj is target f op,max Therefore, it increases to the limit of formula 22 (equation 22). 【0076】 Next, we will explain the stability check. An AEF is essentially a feedback system with analog inputs and analog outputs, and its stability must be carefully designed and guaranteed. If the system is unstable, it may oscillate even without an EUT noise source. Feedback stability can be verified by the phase and gain margin of the loop gain. To derive the loop gain from the circuit model in Figure 4, the feedback loop is isolated from the output of the op-amp, and a test voltage source V is drawn from the isolated node. t The voltage V of the noise source is applied to the injection transformer. nG With the test voltage V not applied, t Voltage V at the pre-node of the CM choke in Ratios can be calculated as shown in equation 28 (equation 28). JPEG0007875639000033.jpg34170 Here, JPEG0007875639000034.jpg42170 【0077】 (V in,amp / V in ) and (V out,amp / V in,ampThe voltage gains of ) are G1(s) and G in equations 9 and 10, respectively. amp It is induced in (s). Therefore, the loop gain of the system can be expressed as in equation 30. JPEG0007875639000035.jpg31170 【0078】 R C and C C The purpose of using it is the effective inductance L of the choke. cm,eff and the effective capacitance C of the Y capacitor branch Y,eff Resonance between G and G poses a risk of instability in the low-frequency range for stability. loop This increases the phase margin of (s). Resonant frequency JPEG0007875639000036.jpg14170 determines the low-frequency boundary of the filter operation, which must be lower than the CE standard low-frequency limit in a proper EMI filter design. C and C C The maximum amount of phase compensation is calculated as shown in Equation 31 (Equation 31). JPEG0007875639000037.jpg32170 Formula 31 (Equation 31) is frequency This occurs with JPEG0007875639000038.jpg20170. 【0079】 JPEG0007875639000039.jpg34170JPEG0007875639000040.jpg31170 【0080】 The expressions for equations 31 (equation 31) and 32 (equation 32) are in R c and C c We provide design guidelines. 【0081】 In equation 28, G2(s) represents the impedance Z of the EUT noise source. n Since it changes depending on Z, it is important to note that the loop gain in equation 30 (equation 30) is similar. nIt can be seen that the larger the magnitude of Z, the greater the loop gain and the smaller the gain margin tends to be. Therefore, Z n Designing stability by setting Z to an infinite value generally provides stability under worst-case conditions. Therefore, in this specification, the loop gain of the designed AEF is set to an infinite value to ensure stability in any EUT application. n Perform calculations or measurements based on the given conditions. 【0082】 Figures 8A and 8B compare the loop gains, with Figure 8A showing the damping component R. d1 , C d , R d2 and phase compensator R c , C c Figure 8B shows the loop gain in an unstable situation where these components are absent, while Figure 8B shows the loop gain in a stable situation where these components are present. 【0083】 For example, AEF is a filter G loop (s) can be expressed using equation 30 (equation 30) as shown in Figure 8. Bypass branch and phase corrector R d1 , C d , R d2 , R c , C c Although it is not present in Figure 8A, it is present in Figure 8B. The effect of these on stability is clearly evident. In Figure 8A, the instability due to the abrupt phase shift around 10 MHz is caused by the secondary winding of the injection transformer, while in Figure 8B, it is resolved by the bypass branch. At low frequencies below 100 kHz in Figure 8A, L cm,eff and C Y,eff Resonance between them also poses a risk of instability due to excessive phase shift. As can be seen in Figure 8B, the phase compensator R c and C c Using this method significantly increases the profit margin. 【0084】 Next, we will discuss the selection of the operational amplifier and the general design procedure. The operational amplifier's high-frequency limit f in the non-inverting amplifier section. OPamp This is the CE standard high frequency limit fCE,max It must be higher. JPEG0007875639000041.jpg22170 【0085】 Furthermore, the voltage and current capacitance of the operational amplifier must be sufficient for noise compensation. To calculate the required operational amplifier capacitance, the voltage V at the output of the operational amplifier is... out,amp (s) and current I out,amp (s) is calculated from the circuit model in Figure 4 as shown in equations 34 and 35, respectively. JPEG0007875639000042.jpg24170JPEG0007875639000043.jpg37170Here, JPEG0007875639000044.jpg31170 【0086】 V in (s) is not only the filter impedance including AEF, but also Z n and V in Since it is determined by (s), the information about the noise source model is V out,amp (s) and I out,amp (s) is necessary to estimate the operating SMPS, Z n and V n The noise source model for (s) can be extracted using various measurement methods that have already been developed. n and V n When (s) is extracted, the OP-amp output voltage V out,amp (t) and output current i out,amp The time-domain waveform of (t) is given by V, which is given by equations 34 (Equation 34) to 36 (Equation 36). out,amp (s) and I out,amp It can be calculated from the spectrum. Therefore, the output voltage capacitance V of the operational amplifier OPamp,max and current capacity i OPamp,max These are the calculated V out,amp (t) and i out,amp It must be sufficient to provide (t). JPEG0007875639000045.jpg24170JPEG0007875639000046.jpg27170 【0087】 I out,amp Since (s) is defined in the half-citcuit model, the actual current flowing through the operational amplifier is twice the calculated current, as shown in Equation 38. 【0088】 As shown in equation 35 (equation 35), out,amp From among the various design elements that affect (s), N inj Increasing this will result in I in the AEF operating frequency range. out,amp (s) increases significantly. inj The voltage gain of the injection transformer, as mentioned earlier, can reduce the output voltage of the operational amplifier instead of increasing the output current. The injection transformer not only isolates the AEF ground from the SMPS ground, but also provides gain and additional design flexibility for the operational amplifier circuit. 【0089】 Next, another embodiment of the isolated active EMI filter according to the present invention, which does not involve the addition of elements to the power line, will be described. Figure 9 is a circuit diagram showing a second embodiment of the isolated active EMI filter according to the present invention, which does not involve the addition of elements to the power line. The second embodiment of the isolated active EMI filter according to the present invention, which does not involve the addition of elements to the power line, comprises a common-mode (CM) choke 1710, a Y capacitor 1720, a transformer 1750, an amplifier 1740, and a compensation winding 1730. 【0090】 Referring to Figure 9, the common-mode (CM) choke 1710 is located on the power supply side, and the live line and neutral line, which are connected to the EMI source, are each wound around it. 【0091】 The Y capacitor 1720 is located on the EMI source side that generates EMI, and consists of two capacitors connected in series. These two capacitors are connected in parallel between the live line and the neutral line and are also connected to ground. 【0092】 The transformer unit 1750 is located before the Y capacitor 1720, and its primary coil senses the noise voltage of the Y capacitor and transforms it via the secondary coil, and is isolated from the power line. 【0093】 The amplification unit 1740 amplifies the noise voltage detected and transformed by the voltage transformation unit 1750. 【0094】 The compensation winding 1710 is wound in a coil over the common mode choke 1710 and injects the noise signal amplified by the amplification section into the common mode choke 1710. 【0095】 Figure 10 is a circuit diagram showing a third embodiment of an isolated active EMI filter according to the present invention, which does not involve the addition of elements to the power line, and comprises a common-mode (CM) choke 1810, a Y capacitor 1820, a detection winding 1830, an amplification unit 1840, and a voltage transformer 1850. 【0096】 Referring to Figure 10, the common mode choke 1810 is positioned on the EMI source side that generates EMI, and the live line (L) and neutral line (N) connected to the EMI source are each wound around it. 【0097】 The Y capacitor 1820 is located on the power supply side to which power is supplied, and consists of two capacitors connected in series. These two capacitors are connected in parallel between the live line L and the neutral line N, and are also connected to earth. 【0098】 The detection winding 1830 is wound in a coil over the common mode choke 1810 and detects the noise current of the common mode choke 1810. 【0099】 The amplification unit 1840 amplifies the noise current detected via the detection winding 1830. 【0100】 The transformer unit 1850 is located before the Y capacitor 1820. The primary coil receives the signal amplified by the amplifier unit 1840, and the secondary coil is connected to ground connected to the Y capacitor 1820 and isolated from the power line. The transformed signal is injected into the Y capacitor 1820 as a compensation signal via the secondary coil. 【0101】 Figure 11 is a circuit diagram showing a fourth embodiment of an isolated active EMI filter according to the present invention, which does not involve the addition of elements to the power line, and comprises a common-mode (CM) choke 1910, a Y capacitor 1920, a transformer 1930, an amplifier 1940, and a compensation winding 1950. 【0102】 Referring to Figure 11, the common mode choke 1910 is positioned on the EMI source side that generates EMI, and the live line (L) and neutral line (N) connected to the EMI source are each wound around it. 【0103】 The Y capacitor 1920 is located on the power supply side to which power is supplied, and consists of two capacitors connected in series, the two capacitors being connected in parallel between the live line and the neutral line and also connected to ground in common. 【0104】 Transformer 1930 is installed before Y capacitor 1920, and its primary coil senses the noise voltage of Y capacitor 1920 and transforms it via the secondary coil, while being isolated from the power line. 【0105】 The amplification unit 1940 amplifies the noise voltage transformed by the transformer 1930. 【0106】 The compensation winding 1950 is wound in a coil over the common mode choke 1910 and injects the noise signal amplified by the amplification unit 1940 into the common mode choke 1910 as a compensation signal. 【0107】 Figure 12 is a flowchart showing a method for reducing EMI noise by adding an active element to a passive EMI filter, corresponding to a first embodiment of an isolated active EMI filter according to the present invention that does not involve adding elements to the power line. 【0108】 Referring to Figures 1 and 12, first, a passive EMI filter is provided, with a common mode choke 110 located on the power supply side and a Y capacitor 120 located on the EMI source side (step S2010). That is, the common mode choke 110 is located on the power supply side to which power is supplied, and the live line and neutral line connected to the EMI source are wound around it. The Y capacitor 120 is located on the EMI source side that generates EMI, and consists of two capacitors connected in series, with the two capacitors connected in parallel between the live line L and the neutral line N and also connected to earth. 【0109】 The EMI noise current of the common mode choke 110 is detected via a detection winding 130, which is wound around the common mode choke 110 in a coil (step S2020). The amplification unit 140 amplifies the EMI noise current detected by the detection winding 130 (step S2030). The signal amplified by the amplifier 140 is received via the primary coil of the transformer 150, which is located before the Y capacitor 120 (step S2040). Then, it is transformed via the secondary coil of the transformer 50 and injected into the Y capacitor 120 (step S2050). Here, the secondary coil of the transformer 150 is connected to the ground connected to the Y capacitor 120 and is isolated from the power line. 【0110】 Figure 13 is a flowchart illustrating a method for reducing EMI noise by adding an active element to a passive EMI filter, corresponding to a second embodiment of an isolated active EMI filter according to the present invention that does not involve adding elements to the power line. Referring to Figures 9 and 13, first, the passive EMI filter comprises a common mode choke 1710 located on the power supply side and a Y capacitor 1720 located on the EMI source side (step S2110). More specifically, the common mode choke 1710 is located on the power supply side to which power is supplied, and the live line (L) and neutral line (N) connected to the EMI source are wound around it. The Y capacitor 1720 is located on the EMI source side that generates EMI, and consists of two capacitors connected in series, with the two capacitors connected in parallel between the live line L and the neutral line N and commonly connected to ground. 【0111】 The primary coil of the transformer 1750, which is located upstream of the Y capacitor 1720, senses the noise voltage using the Y capacitor 1720 as a detection capacitor (step S2120). The sensed noise voltage is transformed via the secondary coil of the transformer 1750 (step S2130). Here, the secondary coil of the transformer 1750 is connected to the ground connected to the Y capacitor 1720 and is isolated from the power line. 【0112】 The amplification unit 1740 amplifies the voltage transformed by the secondary coil of the transformer 1750 (step S2140). The amplified signal is injected into the common mode choke via a compensation winding 1730, which is wound around the common mode choke with a coil (step S2150). 【0113】 Figure 14 is a flowchart showing a method for reducing EMI noise by adding an active element to a passive EMI filter, corresponding to a third embodiment of an isolated active EMI filter according to the present invention that does not involve adding elements to the power line. 【0114】 Referring to Figures 10 and 14, first, a passive EMI filter is provided, with a common mode choke 1810 located on the EMI source side and a Y capacitor 1820 located on the power supply side (step S2210). More specifically, the common mode choke 1810 is located on the EMI source side that generates EMI, and the live line (L) and neutral line (N) connected to the EMI source are wound around it. The Y capacitor 1820 is located on the power supply side where power is supplied, and consists of two capacitors connected in series, with the two capacitors connected in parallel between the live line L and the neutral line N and also connected to earth. 【0115】 A detection winding 1830, which is wound around the common mode choke 1810 with a coil, detects the noise current of the common mode choke 1810 (step S2220). An amplification unit 1840 amplifies the noise current detected by the detection winding 1830 (step S2230). 【0116】 The signal amplified by the amplifier 1840 is input to the primary coil of the transformer 1850, which is located before the Y capacitor 1820 (step S2240). Subsequently, the signal input to the primary coil is transformed via the secondary coil of the transformer 1850 and injected into the Y capacitor 1820 as a compensation signal (step S2250). Here, the secondary coil of the transformer 1850 is connected to the ground connected to the Y capacitor 1820 and is isolated from the power line. 【0117】 Figure 15 is a flowchart illustrating a method for reducing EMI noise by adding an active element to a passive EMI filter, corresponding to a fourth embodiment of an isolated active EMI filter according to the present invention that does not involve adding elements to the power line. Referring to Figures 11 and 15, first, the passive EMI filter is provided, with a common mode choke 1910 located on the EMI source side and a Y capacitor 1920 located on the power supply side (step S2310). More specifically, the common mode choke 1910 is located on the EMI source side that generates EMI, and the live line (L) and neutral line (N) connected to the EMI source are wound around it. The Y capacitor 1920 is located on the power supply side to which power is supplied, and consists of two capacitors connected in series, with the two capacitors connected in parallel between the live line L and the neutral line N and commonly connected to earth. 【0118】 The primary coil of the transformer 1930, which is placed before the Y capacitor 1920, senses the noise voltage of the Y capacitor 1920 (step S2320). The noise voltage sensed by the primary coil is transformed via the secondary coil of the transformer 1930 (step S2330). Here, the secondary coil of the transformer 1930 is connected to the ground connected to the Y capacitor 1920 and is isolated from the power line. 【0119】 The amplification unit 1940 amplifies the noise voltage transformed by the secondary coil (step S2340). The amplified noise signal is injected into the common mode choke 1910 as a compensation signal via a compensation winding 1950 which is wound in a coil over the common mode choke 1910 (step S2350). 【0120】 As described above, the isolation-type active EMI filter according to the present invention, which does not require the addition of elements to the power line, is an active filter that is added to a conventional passive EMI filter consisting of a common-mode choke and a Y capacitor. In this invention, a choke element is proposed that is added to the power line by winding a wire for noise detection and compensation over the common-mode choke present in the passive EMI filter. By using the Y capacitor present in the passive EMI filter as a compensation or detection capacitor and providing a small transformer before the compensation or detection capacitor, the active circuit is isolated from the power line, thus offering the advantage of isolation from the power line without adding any elements to the power line. 【0121】 The isolated active EMI filter according to the present invention winds the detection and compensation wires in an optimal number of turns so as not to degrade the noise attenuation performance of the passive EMI filter itself. The transformer turn ratio is adjusted so as to optimize the noise detection and compensation performance of the Y capacitor and the small transformer preceding it, thereby optimizing the gain of the active filter amplification section. Various stability compensation circuits may be added to ensure the feedback stability of the overall feedback circuit structure for noise detection and compensation. The active EMI filter according to the present invention has a feedback circuit structure that detects noise and injects a compensation signal. 【0122】 According to embodiments of the present invention, when only passive filters are used, the conducted noise in the low-frequency band is reduced by 11 dB, but when the active EMI filter (AEF) of the present invention is additionally installed, it is reduced by 26 dB. When only passive filters are used, expensive common-mode chokes must be used or the total number of filter stages must be increased to adequately attenuate the noise in the low-frequency band. 【0123】 Although the present invention has been described with reference to the embodiments shown in the drawings, these are merely illustrative, and a person with ordinary skill in the art will understand that a wider variety of modifications and equivalent other embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical idea of ​​the appended claims.

Claims

[Claim 1] In a method of reducing noise using an isolated active EMI filter, The aforementioned active EMI filter is A detection winding is wound in a coil over a common mode choke, which has two power lines connected to the EMI source, each wound with a winding. An amplification unit connected to the detection winding, A transformer connected to the aforementioned amplification unit, A Y-capacitor, with both ends connected to the two power lines and the secondary winding of the transformer connected between its midpoint and ground, Includes, The steps include sensing the noise current of the common mode choke through the detection winding, The amplification unit amplifies the sensed noise current, The primary winding of the transformer receives the amplified signal from the amplifier section, The steps include: transforming the amplified signal of the secondary winding of the transformer and outputting it as a compensation signal to the Y capacitor; Methods that include... [Claim 2] Number of turns of the detection winding (N ｓｅｎ ) is the capacitance of the parasitic circuit of the common mode choke, C ｃｍ The capacitance of the parasitic circuit of the detection winding is set to C. ｓｅｎ In that case, 2C ｃｍ / C ｓｅｎ Smaller than the square root of The method according to claim 1. [Claim 3] The active EMI filter further includes a phase compensator connected between the detection winding and the output terminal of the amplifier, configured to increase the phase margin of the feedback loop of the active EMI filter when a noise current sensed through the detection winding in the low-frequency range of less than 100 kHz is input to the amplifier. The method according to claim 1. [Claim 4] The active EMI filter further includes a low-pass filter, one end of which is connected to the detection winding and the other end of which is connected to the amplification unit, for preventing resonance of the detection winding in the high-frequency range of 100 kHz or higher. The method according to any one of claims 1 to 3. [Claim 5] The impedance (Z) viewed from the input terminal of the amplifier towards the low-pass filter side ｉｎ，ＡＥＦ ) is the parasitic RC component impedance (Z) of the detection winding. ｓｅｎ，ｐａｒａ ) characterized by being set higher than The method according to claim 4. [Claim 6] The active EMI filter further includes a bypass branch positioned between the Y capacitor and the transformer to prevent resonance between the EMI source impedance and the Y capacitor. The method according to claim 4. [Claim 7] The cut-off frequency (1 / 2πR ｆ C ｆ ) of the low-pass filter is greater than the maximum operating frequency (f ｏｐ，ｍａｘ ) determined by the inductance of the transformer and the capacitance of the bypass branch, (k ｓｅｎ The coupling coefficient of the detection winding, N ｓｅｎ L is the number of turns of the detection winding. ｃｍ The inductance of the common mode choke is C. ｓｅｎ It is characterized by being smaller than the capacitance of the parasitic circuit of the detection winding. The method according to claim 6. [Claim 8] The effective capacitance of the Y capacitor is at least the number of turns (N) of the detection winding. ｓｅｎ ), the winding ratio (N) between the primary winding and the secondary winding of the transformer. ｉｎｊ ) and the gain of the amplification unit, which is characterized by being determined by these factors. The method according to claim 7.

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