A common mode differential model active noise suppression circuit

Abstract

The invention belongs to the technical field of power electronics, and relates to a common-mode differential-switching model active noise suppression circuit, comprising: a detection link, an amplification link, an injection link and a current-passing link; wherein the detection link detects the voltage of the earth, does not require a capacitor, and is directly connected to the inverting input end of an operational amplifier through a resistor for detection; the operational amplifier in the amplification link uses an N line as a reference, that is, the in-phase input end is connected to the N line, and the operational amplifier amplifies the voltage signal on the N line; the injection link mainly uses an RC circuit composed of a resistor and a capacitor to convert the voltage signal output by the operational amplifier into a compensation current and inject it back into the earth; the current-passing link uses a differential mode capacitor to provide a return path for the compensation current while balancing the compensation currents of two branches, and can attenuate the differential mode noise of the system; the invention can convert common mode noise into differential mode noise, and reduce the common mode noise while attenuating the differential mode noise.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics and relates to a common-mode differential model active noise suppression circuit. Background Art

[0002] With the rapid development of the electronics industry, the increase in switching frequency has become a major trend. Although this progress has significantly improved efficiency and made components more miniaturized, it has also brought a series of new challenges, especially in terms of electromagnetic interference (EMI). High-frequency switching operations will produce stronger electromagnetic radiation, and more compact component placement will also bring greater near-field interference. These interferences not only affect the normal operation of the equipment itself, but may also interfere with peripheral equipment and even threaten the stability of the communication system; for grid-connected systems, excessive electromagnetic interference will also affect the safety and reliability of the power grid. Therefore, how to effectively suppress EMI has become an important technical problem in the electronics industry.

[0003] In the process of dealing with EMI problems, the design and optimization of EMI filters are crucial. As the main means of suppressing electromagnetic interference, EMI filters can effectively reduce the propagation of high-frequency signals, reduce interference to sensitive circuits and external devices, and provide key support for ensuring the stability of electronic equipment. Traditional EMI filters are divided into passive and active types. Passive EMI filters are widely used in industry due to their simplicity, reliability, high stability and low cost. However, in order to achieve effective low-frequency interference suppression, passive EMI filters usually require larger inductance and capacitance, which limits the size of the filter in some applications, especially in modern electronic devices that pursue miniaturization. In addition, due to the booming semiconductor chip industry, the cost advantage of passive EMI filters is not significant enough. On the contrary, active EMI filters are gradually being widely used due to their better low-frequency suppression effect, smaller size and adjustable performance.

[0004] Active EMI filter (AEF) is mainly composed of three parts: noise detection, noise amplification and noise compensation. The noise detection part has two methods: current detection and voltage sampling. The noise compensation part and current sampling also have two methods: current compensation and voltage compensation. Therefore, according to the difference between the detection part and the compensation part, the active EMI filter can be divided into current-sensing current-compensating type (CSCC), current-sensing voltage-compensating type (CSVC), voltage-sensing current-compensating type (VSCC), and voltage-sensing voltage-compensating type (VSVC). Since current detection requires the use of current transformers and voltage compensation requires the use of transformers, both of which require a large volume, the use of voltage-sensing current-compensating active EMI filters can achieve a smaller volume.

[0005] Active EMI filters are divided into common mode AEF and differential mode AEF according to the type of attenuated noise. Their working principles and design methods are basically similar, but the specific compensation paths are different. Among them, since the attenuation of common mode noise is limited by factors such as ground leakage current, common mode inductor volume and high frequency characteristics, it is more difficult to design passive EMI filters. Therefore, the industry has been seeking to use active EMI filters to suppress common mode noise.

[0006] The structure of the traditional VSCC active EMI filter is to obtain the common mode voltage by superimposing the signals detected on the L line and the N line, and then reversely amplify it through the operational amplifier, and finally inject it back to the L line and the N line to compensate the noise signal. The operational amplifier is referenced to the ground, and the detection and injection points are both on the L line and the N line.

[0007] However, the existing common-mode AEF has two obvious disadvantages. The first disadvantage is that the common-mode signal is detected directly from the L line and the N line. The voltage on the L line is relatively high. When the voltage on the L line fluctuates, the input voltage of the operational amplifier fluctuates accordingly, which will affect the stability of the operational amplifier and the AEF system. The second disadvantage is the high cost. The traditional AEF requires four capacitors. A large number of capacitors will not only affect the stability of the system, but also increase the cost.

[0008] Therefore, how to enhance the stability of the operational amplifier and the AEF system without increasing the cost is a technical problem that the AEF system needs to solve urgently. Summary of the invention

[0009] The technical solution adopted by the present invention to solve the technical problem is: a common-mode differential model active noise suppression circuit, including: a detection link, an amplification link, an injection link and a current-passing link;

[0010] The detection link is composed of a detection resistor; the voltage of the earth is detected without a capacitor, and is directly connected to the inverting input terminal of the operational amplifier through the detection resistor for detection; one end of the detection resistor is connected to the earth, and the other end is connected to the inverting input terminal of the operational amplifier;

[0011] The amplification link is composed of an operational amplifier and a feedback resistor; the operational amplifier uses the N line as a reference, that is, the non-inverting input terminal is connected to the N line, the feedback resistor is connected across the inverting input terminal and the output terminal of the operational amplifier, and the operational amplifier amplifies the voltage signal on the N line; the non-inverting input terminal of the operational amplifier is connected to the N line, the inverting input terminal of the operational amplifier is connected to the detection resistor and the feedback resistor, the reference ground between the positive and negative poles of the power supply is connected to the N line, and the output terminal is connected to the injection resistor and the feedback resistor;

[0012] The injection link is composed of an injection resistor and an injection capacitor. The injection resistor and the injection capacitor are connected in series to form a high-pass filter, which converts the voltage signal output by the operational amplifier into a compensation current and injects it back into the ground; one end of the injection resistor is connected to the output end of the operational amplifier, and the other end of the injection resistor is connected to the injection capacitor. One end of the injection capacitor is connected to the injection resistor, and the other end of the injection capacitor is connected to the ground.

[0013] The through-current link is composed of differential mode capacitors. The through-current link provides a return path for the compensation current while balancing the compensation current of the two branches, and can attenuate the differential mode noise of the system. One end of the differential mode capacitor is connected to the L line between the LISN and the EUT, and the other end of the differential mode capacitor is connected to the N line between the LISN and the EUT.

[0014] The working process of the common-mode-to-differential model active noise suppression circuit is: converting common-mode noise into differential-mode noise, and attenuating the common-mode noise while attenuating the differential-mode noise;

[0015] The connection method of the common-mode to differential model active noise suppression circuit is as follows: the power supply is connected to the device under test (EUT) after passing through the LISN, and a differential mode capacitor C is connected in series between the L line and the N line of the device under test (EUT). x .

[0016] The N line of the EUT is connected to the same-direction input terminal of the operational amplifier, and the inverse input terminal of the operational amplifier is connected in series with a resistor R s Then connected to GND as a sampling link, the output end of the operational amplifier is connected in series with resistor R inj , capacitor C injAfter that, it is connected to GND as a compensation link. A capacitor R is also connected between the reverse input terminal of the operational amplifier and the output terminal of the operational amplifier. f As an amplification link.

[0017] Preferably, the detection link only needs to use a conventional detection resistor and does not need to use a resistor in series with a capacitor for detection, thereby removing the capacitor in the traditional detection circuit.

[0018] Preferably, the operational amplifier in the amplification link uses the N line of the EUT device power supply circuit as a reference, rather than using the ground line GND of the EUT device power supply circuit as a reference.

[0019] Preferably, the return path of the compensation current output by the injection link is: first injected into the ground wire GND of the EUT equipment power supply line, and then flows into the L line and N line of the EUT equipment power supply line through the LISN, wherein the compensation current flowing into the L line then flows back to the N line through the differential mode capacitor of the current-passing link.

[0020] Preferably, the differential mode capacitor of the current-passing link is a capacitor of μF level to balance the compensation current of the two branches.

[0021] Preferably, in the common-mode differential-mode active noise suppression circuit, the equivalent common-differential-mode noise currents are respectively:

[0022] (5)

[0023] (6)

[0024] In formula (5) and (6), TN CM TN DM They represent the equivalent common-mode and differential-mode noise currents after CTD-AEF conversion, respectively. DM Represents the raw differential mode current.

[0025] Preferably, in the common-mode slip model active noise suppression circuit, the noise current of the N line flowing through the line impedance stabilization network LISN is:

[0026] (8)

[0027] Compensation current I offset for:

[0028] (9)

[0029] In formula (8) and (9), Z s ,I N represents the equivalent noise source of N lines based on the Norton principle, Z s represents the parallel impedance of the noise current source, IN represents the current generated by the equivalent noise current source, Z LISN Indicates the impedance of the LISN on the N-line branch that needs to be added between the power supply and the target circuit during EMI testing. S represents the total gain of the CTD-AEF system, Z out represents the output impedance of the operational amplifier, Z inj Represents the impedance of the injection link.

[0030] More preferably, in the common mode differential model active noise suppression circuit, the equivalent insertion loss of CM noise after adding CTD-AEF is:

[0031] (10)

[0032] In formula (10), Z Cx Represents the capacitance C of the current-carrying link x The equivalent impedance of k represents the original differential mode current I DM The original common mode current I CM ratio.

[0033] Preferably, the differential mode capacitor C x 1~2.2μF.

[0034] The beneficial effects of the present invention are:

[0035] The current-passing link of the present invention is a μF-level differential mode capacitor, so the present invention can well balance the compensation current of the two branches and effectively attenuate the differential mode noise of the object circuit. After the common mode noise is converted to differential mode noise, the differential mode noise and the common mode noise are attenuated at the same time; therefore, the present invention can convert the common mode noise into differential mode noise, and the greater the gain of the system, the better the conversion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a circuit structure diagram of a common-mode differential model active noise suppression circuit of the present invention;

[0037] Figure 2 It is a common-differential mode noise circulation path diagram of the active noise suppression circuit without adding a common-mode differential model of the present invention;

[0038] Figure 3 It is a common-differential mode noise circulation path diagram of the active noise suppression circuit with added common-mode differential model of the present invention;

[0039] Figure 4 This is an equivalent EMI model diagram of the common-mode differential model active noise suppression circuit of the present invention with respect to the N line;

[0040] Figure 5is a signal flow diagram of the common-mode-slip model active noise suppression circuit system of the present invention;

[0041] Figure 6 It is a structural diagram of the active noise suppression circuit of the real common-mode differential model of the present invention;

[0042] Figure 7 This is a physical diagram of the common-mode differential model active noise suppression circuit of the present invention;

[0043] Figure 8 This is a standard test environment diagram for testing common mode noise of the present invention;

[0044] Fig. 9 This is a diagram showing the common mode noise suppression effect of CTD-AEF under the standard test environment of the present invention;

[0045] Fig.10 This is a diagram showing the common mode noise suppression effect of CTD-AEF on FSBB of the present invention;

[0046] Fig.11 It is a diagram showing the differential mode noise suppression effect of CTD-AEF on FSBB of the present invention.

[0047] In the figure, 101 is a LISN; 102 is an EUT; 103 is a differential mode capacitor; 104 is an operational amplifier; 105 is an injection resistor; 106 is an injection capacitor; 107 is a detection resistor; and 108 is a feedback resistor. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] refer to Figures 1 to 11 In this embodiment, the common mode differential model active noise suppression circuit (hereinafter referred to as CTD-AEF) has a structure as shown in FIG. Figure 1 The figure shows the following parts: detection link, amplification link, injection link and current-passing link. The detection link uses a resistor to directly detect the voltage of the ground; the operational amplifier in the amplification link uses the N line as a reference, that is, the in-phase input terminal is connected to the N line, and the operational amplifier amplifies the voltage signal on the N line; the injection link mainly uses an RC circuit composed of a resistor and a capacitor to convert the voltage signal output by the operational amplifier into a compensation current and inject it back into the ground; the current-passing link has two functions, one is to provide a return path for the compensation current, and the other is to attenuate the differential mode noise of the system.

[0050] like Figure 2 As shown in the figure, when the system does not add CTD-AEF, the common-mode noise current amplitudes on the L line and the N line are equal and in the same direction; the differential-mode noise current amplitudes are equal and in opposite directions. Therefore, the current and voltage on the L line and the N line are:

[0051] (1)

[0052] (2)

[0053] like Figure 3 The CTD-AEF shown uses the N line as a reference, detects the voltage of GND, reversely amplifies it through the operational amplifier, and then injects the compensation current back to GND through the injection link. A part of the compensation current flows directly back to the N line through the LISN, and the other part flows to the L line and then passes through the current-passing link and finally returns to the N line. The noise current on the L line and the N line converted by the CTD-AEF is:

[0054] (3)

[0055] (4)

[0056] TN L TN N TN CM TN DM They are respectively the L line, N line, equivalent common mode, and equivalent differential mode noise current after CTD-AEF conversion.

[0057] Combining equations (3) and (4), we can obtain that the equivalent common-mode and differential-mode noise currents after conversion are:

[0058] (5)

[0059] (6)

[0060] Next, from the perspective of small signal analysis, we will establish an equivalent EMI model of CTD-AEF and derive the noise current of L line and N line. First, derive the noise of N line, such as Figure 4 As shown, Z s ,I N is the equivalent noise source of the N line based on the Norton principle. The CTD-AEF model can be replaced by the VSCC type AEF model. LISN For EMI testing, it is necessary to add the impedance of the linear impedance stabilization network between the power supply and the target circuit. S represents the total gain of the CTD-AEF system, V out and Z out are the output voltage and output impedance of the operational amplifier, Z injis the impedance of the injection link. The current flowing through the N line through the LISN is I p , the compensation current of CTD-AEF is I offset The equivalent signal flow diagram of the entire system is as follows: Figure 5 shown.

[0061] Through this model, the compensation current can be obtained as:

[0062] (7)

[0063] according to Figure 5 The signal flow graph shown can be used to deduce that the noise current flowing through the N line through the LISN is:

[0064] (8)

[0065] Substituting formula (8) into formula (7), we can obtain:

[0066] (9)

[0067] You can see G S The bigger I p The smaller, when hour, , , which is consistent with the above analysis of the N-line noise current path.

[0068] The attenuation of DM noise is mainly due to C S Therefore, the insertion loss of DM noise is not discussed here. Here we mainly discuss the equivalent insertion loss of CM noise after adding CTD-AEF, and the formula is as follows:

[0069] (10)

[0070] Where Z Cx is the capacitance C S The equivalent impedance of DM with I CM From equation (10), it can be seen that the equivalent CM noise insertion loss of CTD-AEF is related to k and G S The smaller k is, the stronger the CM noise attenuation capability is. S The larger it is, the stronger the ability of CM noise to be converted into DM noise.

[0071] Differential mode capacitance C of the return path x Generally, it is of μF level. xWhen 1μF is used, the impedance is 1Ω at 150kHz, which is very small compared to the 50Ω impedance of LISN. Therefore, the return path of the compensation current on the L line and the N line can be regarded as balanced, and the compensation current flowing back to the L line and the N line is equal. Figure 5 , we can get the current I flowing through the LISN of the L line q for:

[0072] (11)

[0073] when When, due to ,so:

[0074] (12)

[0075] This is consistent with the above analysis of the L line noise current path.

[0076] Therefore, it can be concluded that CTD-AEF can convert common-mode noise into differential-mode noise, and the greater the system gain, the better the conversion effect. It can be noted that the current-passing link in CTD-AEF is a μF-level differential-mode capacitor, which can well balance the compensation current of the two branches and effectively attenuate the differential-mode noise of the target circuit. Therefore, the entire CTD-AEF system reduces the common-mode noise while attenuating the differential-mode noise.

[0077] CTD-AEF has the following differences compared to traditional VSCC common mode AEF:

[0078] 1.CTD-AEF uses only two capacitors, while the traditional VSCC common-mode AEF requires four capacitors

[0079] 2. The op amp in CTD-AEF uses the N line as reference, while the op amp in the traditional VSCC common mode AEF uses GND as reference

[0080] 3.CTD-AEF detection and injection are only performed on the N line and GND, operating in a low-voltage environment; while the detection and injection of the traditional VSCC type common-mode AEF are performed on the L line and N line. The stability of CTD-AEF is more guaranteed.

[0081] 4. Compared with the traditional VSCC type common-mode AEF, CTD-AEF effectively attenuates both common-mode and differential-mode noise.

[0082] Design the parameters in CTD-AEF. First, the detection link needs to detect high-frequency components to prevent the power frequency components from entering. Unlike the traditional VSCC-AEF, the detection link of CTD-AEF does not use RC branches. The detection link directly connects the ground wire to Rs to detect the ground voltage. There is no need to use a high-pass filter composed of RC branches to detect the ground voltage.

[0083] For the signal amplification link, due to the limitation of the gain-bandwidth product of the operational amplifier, the gain should not be too large. Here, the operational amplifier AD829 is selected, which has a bandwidth of 120MHz, a slew rate of 230V / μs, and a supply voltage of ±5V-±15V. , .

[0084] For the injection link, only the high-frequency compensation current is allowed to pass through to suppress the high-frequency EMI noise current. The appropriate output resistor should be selected according to the device manual of the operational amplifier. Here, , , cutoff frequency .

[0085] For the current flow link, you can choose a μF level capacitor. Here we choose .

[0086] In the actual circuit, in order to improve the current driving capability of the op amp, an additional push-pull circuit is added.

[0087] Figure 6 The circuit schematic diagram based on the above design is shown, and the parameters and models of all devices are shown in Table 1. Figure 7 Shows the Figure 6 The actual product made by the circuit can be seen to be very small, only 1.7×2.1CM, about the size of a coin, much smaller than the traditional VSCC-AEF.

[0088]

[0089] Here, two examples of the CTD-AEF common-mode noise suppression effect are verified. The first is the test results under a standard environment, and the second is the results verified in a four-switch buck-boost topology.

[0090] The test in the standard test environment mainly uses a signal generator and a stable 50Ω impedance to simulate the flow of noise. The test configuration of CM noise is as follows: Figure 8 As shown in the figure, two channels of the signal generator are used to simultaneously send out noise signals with the same amplitude, frequency and phase to simulate common mode noise, and then an EMI receiver is used to detect it on the 50Ω resistor side. The test results are shown in the figure. Fig. 9It can be seen that after adding CTD-AEF, the common mode noise of the entire frequency band is attenuated by 10-20dB.

[0091] Since CTD-AEF has good performance in a standard test environment, it is tested in an actual noise environment. In the test of the actual circuit, this example uses the relatively new four-switch buck-boost circuit (FSBB). The working condition of this DC-DC circuit is 48Vdc to 48Vdc, the output current is 1A, and the power is 48W. The switching frequency is about 200kHz. The supply voltage of CTD-AEF is ±5V, which is provided by an additional DC power supply. A noise separator is used to convert the noise on the power line into common-mode or differential-mode noise. The test results are as follows Fig.10 As shown in the figure, it can be seen that after adding CTD-AEF, the common mode noise of the entire frequency band is attenuated by 10-20dB. x CTD-AEF also has a great attenuation effect on differential mode noise. Fig.11 The figure shows the attenuation effect on DM noise. It can be seen that after adding CTD-AEF, the differential mode noise in the full frequency band is attenuated by more than 30dB.

[0092] In summary, the current-passing link of the present invention is a μF-level differential mode capacitor, so the present invention can well balance the compensation current of the two branches, and can also effectively attenuate the differential mode noise of the object circuit. After the common mode noise is converted to differential mode noise, the differential mode noise and the common mode noise are attenuated at the same time; the present invention can convert the common mode noise into differential mode noise, and the greater the gain of the system, the better the conversion effect. Therefore, the present invention has a wide range of application prospects in improving the stability of active EMI filters.

[0093] It should be emphasized that the above are only preferred embodiments of the present invention and do not impose any form of limitation on the present invention. Any simple modification of the above embodiments based on the technical essence of the present invention also falls within the protection scope of the present invention. Other equivalent changes and modifications still fall within the scope of the technical solution of the present invention.

Claims

1. A common mode differential model active noise suppression circuit, characterized in that: include: Detection link, amplification link, injection link and flow link; The detection link is composed of a detection resistor (107); the voltage of the earth is detected without a capacitor, and the detection is performed directly through the detection resistor (107) connected to the inverting input terminal of the operational amplifier (104); one end of the detection resistor (107) is connected to the earth, and the other end is connected to the inverting input terminal of the operational amplifier (104); The amplification link is composed of an operational amplifier (104) and a feedback resistor (108); the operational amplifier (104) uses the N line as a reference, that is, the non-inverting input end is connected to the N line, the feedback resistor (108) is connected across the inverting input end and the output end of the operational amplifier (104), and the operational amplifier (104) amplifies the voltage signal on the N line; the non-inverting input end of the operational amplifier (104) is connected to the N line, the inverting input end of the operational amplifier (104) is connected to the detection resistor (107) and the feedback resistor (108), the reference ground between the positive and negative poles of the power supply is connected to the N line, and the output end is connected to the injection resistor (105) and the feedback resistor (108); The injection link is composed of an injection resistor (105) and an injection capacitor (106), wherein the injection resistor (105) and the injection capacitor (106) are connected in series to form a high-pass filter, which converts the voltage signal output by the operational amplifier (104) into a compensation current and injects it back into the ground; one end of the injection resistor (105) is connected to the output end of the operational amplifier (104), the other end of the injection resistor (105) is connected to the injection capacitor (106), one end of the injection capacitor (106) is connected to the injection resistor (105), and the other end of the injection capacitor (106) is connected to the ground; The current-passing link is composed of a differential mode capacitor (103); the current-passing link balances the compensation currents of the two branches while providing a return path for the compensation current, and can attenuate the differential mode noise of the system; one end of the differential mode capacitor (103) is connected to the L line between the LISN (101) and the EUT (102), and the other end of the differential mode capacitor (103) is connected to the N line between the LISN (101) and the EUT (102); The working process of the common-mode-to-differential model active noise suppression circuit is: converting common-mode noise into differential-mode noise, and attenuating the common-mode noise while attenuating the differential-mode noise.

2. The common mode-slip model active noise suppression circuit according to claim 1, characterized in that: The return path of the compensation current output by the injection link is: first injected into the ground wire GND of the EUT (102) equipment power supply line, and then flows into the L line and N line of the EUT (102) equipment power supply line through the LISN (101), wherein the compensation current flowing into the L line then flows back to the N line through the differential mode capacitor (103) of the current passing link.

3. The common mode-slip model active noise suppression circuit according to claim 1, characterized in that: The differential mode capacitor (103) of the current-passing link is a capacitor of μF level, so as to balance the compensation current of the two branches.

4. The common mode-slip model active noise suppression circuit according to claim 1, characterized in that: In the common-mode differential-mode active noise suppression circuit, the equivalent common-differential-mode noise currents are: （5） （6） In formula (5) and formula (6), TN CM TN DM They represent the equivalent common-mode and differential-mode noise currents after CTD-AEF conversion, respectively. DM Represents the raw differential mode current.

5. The common mode-slip model active noise suppression circuit according to claim 1, characterized in that: In the common-mode slip model active noise suppression circuit, the noise current of the N line flowing through the line impedance stabilization network LISN is: （8） Compensation current I offset for: （9） In formula (8) and formula (9), Z s ,I N represents the equivalent noise source of N lines based on the Norton principle, Z s represents the parallel impedance of the noise current source, I N represents the current generated by the equivalent noise current source, Z LISN It represents the impedance of the linear impedance stabilization network LISN (101) on the N-line branch that needs to be added between the power supply and the target circuit during EMI testing. S represents the total gain of the CTD-AEF system, Z out represents the output impedance of the operational amplifier (104), Z inj Represents the impedance of the injection link.

6. The common mode-slip model active noise suppression circuit according to claim 5, characterized in that: In the common-mode differential model active noise suppression circuit, the equivalent insertion loss of CM noise after adding CTD-AEF is: （10） In formula (10), Z Cx Represents the capacitance C of the current-carrying link x The equivalent impedance of k represents the original differential mode current I DM The original common mode current I CM ratio.

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