Analog active EMI filter with double-ring structure and noise suppression verification method

Abstract

The invention relates to an analog active EMI filter with a double-ring structure and a noise suppression verification method. The EMI filter comprises a direct-current power supply, an LISN circuit, a voltage detection circuit, an injection circuit, an amplification circuit and a switching power supply, the direct-current power supply, the LISN circuit, the voltage detection circuit, the injection circuit and the switching power supply are sequentially connected in parallel, the injection circuit comprises a voltage injection branch and a current injection branch connected with the voltage injection branch in parallel, the voltage injection branch and the current injection branch are used for voltage injection and current injection respectively, and the amplification circuit comprises a first anti-phase amplification branch and a second anti-phase amplification branch connected with the first anti-phase amplification branch in parallel. The first anti-phase amplification branch circuit is respectively connected with the voltage detection circuit and the current injection branch circuit to form a first annular structure, and the second anti-phase amplification branch circuit is respectively connected with the voltage detection circuit and the voltage injection branch circuit to form a second annular structure. Compared with the prior art, the method has the advantages of realizing an effective noise interference suppression effect and the like.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic compatibility technology, and in particular to an analog active EMI filter with a dual-loop structure and a noise suppression verification method. Background Art

[0002] Modern switching power supply technology reduces switching losses by quickly switching power switch tubes. The driving signal waveform used to control the power switch tube is a two-level switching signal. Because of its steep rising and falling edges, as well as the increasingly high switching frequency, it causes rapid changes in voltage and current in the circuit. Since the high-frequency du / dt voltage signal and di / dt current signal react with the high-frequency parasitic parameters in the circuit, electromagnetic interference is generated in the circuit. This electromagnetic interference can affect nearby electronic systems through radiation and conduction, which not only interferes with their normal operation and reduces system reliability, but also may pollute the power grid. At present, different international and domestic electromagnetic compatibility standards generally detect the conducted electromagnetic interference of electronic and electrical products in the frequency band of 150kHz-30MHz, requiring that the noise level of conducted electromagnetic interference be lower than the specified safety value. Considering the hazards of conducted electromagnetic interference and the requirements of electromagnetic compatibility standards for electronic and electrical products, measures need to be taken to reduce the conducted electromagnetic interference in the circuit.

[0003] One of the ways to reduce the conducted electromagnetic interference in the circuit is to consider designing a filter circuit and use insertion loss to quantify and evaluate the filtering effect. Traditionally, passive EMI filters are used to suppress conducted electromagnetic interference. Passive EMI filters are composed of passive components such as resistors, capacitors and inductors to form a passive filter circuit, which is added to the input end of the switching power supply to suppress conducted electromagnetic interference. Because of its simple structure and low cost, it is widely used in various occasions. However, due to the large weight and volume of passive EMI filters, the application of passive EMI filters in high-density power electronic systems faces bottlenecks. Finally, in order to effectively suppress low-frequency conducted EMI, the capacitors and inductors of the passive EMI filter require larger parameters to reduce the cutoff frequency of the passive EMI filter, which increases the volume and cost of the filter circuit. In addition, some high-frequency parasitic parameters of passive components may form resonance in the circuit, which will increase electromagnetic interference at the frequency of resonance and affect the operation of other system parts of the circuit.

[0004] There is currently research on active EMI filters, which can also achieve conducted electromagnetic interference suppression. Active EMI filters have lower weight and volume, are easy to integrate, and can effectively suppress low-frequency conducted EMI. Active EMI filters generally include detection circuits, amplifier circuits, and injection circuits. Active EMI filters can measure conducted electromagnetic interference noise signals, reverse them and inject them into the switching power supply circuit to achieve conducted electromagnetic interference suppression. However, active EMI filters require the gain of the amplifier circuit to be as large as possible and the effective bandwidth to be as wide as possible to achieve a better filtering effect. Active EMI filters generally use operational amplifiers to build amplifier circuits. The larger the gain design of the operational amplifier, the lower its effective bandwidth will be, which will reduce the suppression effect of the active EMI filter on conducted electromagnetic interference. Therefore, active EMI filters have high requirements on the performance of the amplifier circuit, and their effective bandwidth and insertion loss are also limited, and they cannot achieve a good filtering effect.

[0005] Through the above analysis, the problems and defects of the existing technology are as follows: high-frequency du / dt voltage signals and di / dt current signals will cause serious electromagnetic interference (EMI) to the DC converter system, while the passive EMI filter is large in size and weight and is not suitable for applications in high-density power electronic systems. The active EMI filter has high requirements on the performance of the amplification circuit and cannot effectively suppress high-frequency conducted EMI. The bandwidth cannot cover the entire 30MHz conducted EMI frequency band, and the obtained filtering effect is limited. Summary of the invention

[0006] The purpose of the present invention is to provide a dual-loop structured analog active EMI filter and a noise suppression verification method for improving the filtering effect on conducted electromagnetic interference.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] An analog active EMI filter with a dual-ring structure comprises a DC power supply, a LISN circuit, a voltage detection circuit, an injection circuit, an amplifier circuit and a switching power supply; the DC power supply, the LISN circuit, the voltage detection circuit, the injection circuit and the switching power supply are connected in parallel in sequence, the injection circuit comprises a voltage injection branch and a current injection branch connected in parallel therewith, which are used for voltage injection and current injection respectively, the amplifier circuit comprises a first inverting amplifier branch and a second inverting amplifier branch connected in parallel therewith, the first inverting amplifier branch is connected to the voltage detection circuit and the current injection branch respectively to form a first ring structure, and the second inverting amplifier branch is connected to the voltage detection circuit and the voltage injection branch respectively to form a second ring structure.

[0009] Furthermore, the voltage detection circuit uses a first-order RC high-pass circuit to implement voltage detection, and the first-order RC high-pass circuit includes a resistor and a capacitor connected thereto.

[0010] Furthermore, the current injection branch adopts an RC circuit, the RC circuit includes a resistor and a capacitor connected thereto, and the voltage injection branch includes a resistor and three windings connected thereto.

[0011] Furthermore, the first inverting amplifying branch and the second inverting amplifying branch are both constructed based on operational amplifiers, and are used to amplify and output the EMI noise source.

[0012] Furthermore, the first inverting amplification branch and the second inverting amplification branch both include an operational amplifier, an input resistor, a feedback resistor and a grounding resistor, the input resistor is connected to the inverting input terminal of the operational amplifier, the feedback resistor is connected between the output terminal and the inverting input terminal of the operational amplifier, and the grounding resistor is connected to the inverting input terminal of the operational amplifier.

[0013] The present invention also provides a noise suppression verification method for the analog active EMI filter with the dual-ring structure described above, comprising the following steps:

[0014] The analog active EMI filter of the dual-loop structure is modeled as a whole and simplified to obtain a simplified overall circuit model;

[0015] Based on the simplified overall circuit model, the transfer function from the EMI noise source and the output of the amplifier circuit to the LISN circuit is analyzed to build a signal flow graph model;

[0016] According to the signal flow graph model, design parameters of the analog active EMI filter of the dual-loop structure;

[0017] The simulation verification is carried out according to the designed parameters to obtain the verification results.

[0018] Furthermore, the step of obtaining a simplified overall circuit model includes:

[0019] Based on the simulated active EMI filter with a dual-loop structure after overall modeling, the noise source is modeled as a noise voltage source and a source impedance, and the first inverting amplifier branch and the second inverting amplifier branch connected in parallel therewith are simplified as a compensation voltage source to obtain the simplified overall circuit model.

[0020] Furthermore, the parameter design steps include:

[0021] Design the cut-off frequency and resistance and capacitance values ​​of the voltage detection circuit according to the cut-off frequency and impedance of the first-order RC high-pass circuit and the RC circuit;

[0022] According to the resistance value of the noise source impedance, design the parameters of the amplifier circuit, including input resistance, feedback resistance and balance resistance;

[0023] Analyzing the relationship between the insertion loss and the loop gain of the injection circuit according to the signal flow graph model;

[0024] According to the relationship between the insertion loss and the loop gain of the injection circuit, the parameters of the injection circuit are designed to maximize the insertion loss.

[0025] Furthermore, the insertion loss formula is:

[0026]

[0027] in:

[0028]

[0029]

[0030] Where IL is, V 1 (s) is the noise voltage on the LISN circuit (2) before adding the EMI filter, V 2 (s) is the noise voltage on the LISN circuit (2) after adding the EMI filter, G 1 (s), G 2 (s) is the gain of the second inverting amplifier branch (5) and the first inverting amplifier branch (4), Z n is the source impedance, Z j2 The impedance on the primary side of the three windings is expressed as the equivalent resistance on the secondary side, Z l is the impedance of the LISN circuit (2), R s , C s are the resistance and capacitance in the first-order RC high-pass circuit, V n (s) is the noise source, R LISN , C LISN are the resistance and capacitance of the LISN circuit (2).

[0031] Furthermore, the simulation process includes:

[0032] Without obtaining any analog active EMI filter for simulation, the spectrum of the original noise source is obtained;

[0033] Acquire the simulated active EMI filter of the dual-ring structure for simulation, and obtain the spectrum of the EMI noise source when the simulated active EMI filter of the dual-ring structure is working;

[0034] The simulated active EMI filter of the dual-ring structure is obtained, and its amplifying circuit input is short-circuited and then simulated to obtain the spectrum of the EMI noise source when the simulated active EMI filter of the dual-ring structure is not working.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The EMI filter of the present invention is configured as a dual-loop structure, wherein the amplifier circuit is divided into two reverse amplifier branches, and the injection circuit includes a voltage injection branch and a current injection branch. The first reverse amplifier branch is connected to the voltage adopting circuit and the current injection branch respectively to form a first ring structure, and the second reverse amplifier branch is connected to the voltage adopting circuit and the voltage injection branch respectively to form a second ring structure. The two reverse amplifier branches are used to perform inverse amplification of the conducted electromagnetic interference through the dual-loop structure. The voltage injection branch and the current injection branch serve as two feedback branches, and their total amplification gain is the sum of the amplification gains of each branch. By doing so, the gain value of the amplifier circuit can be reduced, and at the same time, the working bandwidth of the two reverse amplifier branches is increased, so that the suppression effect on the conducted electromagnetic interference noise signal will be better, thereby improving the filtering effect on the conducted electromagnetic interference.

[0037] (2) The noise suppression effect of the EMI filter is verified by experiments. Compared with the insertion loss formula of the general active EMI filter, the insertion loss formula of the dual-loop active EMI filter proposed by the present invention has one more term and a larger insertion loss. The insertion loss formula is related to the loop gain of the feedback loop. The larger the loop gain, the larger the insertion loss and the better the filtering effect of the filter. Therefore, the noise suppression effect of the EMI filter of the present invention is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a topology block diagram of a dual-loop analog active EMI filter of the present invention;

[0039] Figure 2 It is a flow chart of the noise suppression verification process of the dual-loop analog active EMI filter of the present invention;

[0040] Figure 3 A topological structure diagram of a dual-loop analog active EMI filter of the present invention;

[0041] Figure 4 It is a signal flow diagram of the dual-loop analog active EMI filter of the present invention;

[0042] Figure 5 It is a simulation principle diagram of the EMI suppression circuit of the present invention;

[0043] Figure 6 This is a comparison diagram of the EMI noise spectrum before and after adding the filter of the present invention;

[0044] Figure 7 This is a time domain waveform comparison diagram of the original EMI noise of the present invention and before and after the filter is added. DETAILED DESCRIPTION

[0045] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0046] This embodiment provides an analog active EMI filter with a dual-loop structure, such as Figure 1 As shown, the filter includes: a DC power supply 1, a LISN circuit 2, a voltage detection circuit 3, an injection circuit, an amplifier circuit and a switching power supply 8. The injection circuit includes a voltage injection branch 7 and a current injection branch 6 connected in parallel therewith, which are used for voltage injection and current injection respectively. The amplifier circuit includes a first inverting amplifier branch 4 and a second inverting amplifier branch 5 connected in parallel therewith. The first inverting amplifier branch is respectively connected to the voltage detection circuit 3 and the current injection branch 6 to form a first ring structure. The second inverting amplifier branch 5 is respectively connected to the voltage detection circuit 3 and the voltage injection branch 7 to form a second ring structure.

[0047] The voltage detection circuit 3 uses an RC circuit to implement voltage detection, forming a first-order high-pass RC filter to detect conducted EMI in the frequency band of 150kHz-30MHz.

[0048] Two inverting amplification branches are built based on operational amplifiers to amplify and output the conducted EMI signal. It includes an operational amplifier, an input resistor, a feedback resistor and a grounding resistor. The input resistor is connected to the inverting input of the operational amplifier, the feedback resistor is connected between the output and the inverting input of the operational amplifier, and the grounding resistor is connected to the inverting input of the operational amplifier. The amplification factor is designed as the ratio of the input resistor to the feedback resistor, and the grounding resistor is the parallel value of the input resistor and the feedback resistor.

[0049] The voltage injection branch 7 and the current injection branch 6 serve as two feedback branches, and the current injection branch 6 is closer to the LISN circuit 2 (serving as the load end). The current injection branch 6 is an RC circuit, and the voltage injection branch 7 is a resistor and three windings.

[0050] The performance of the amplifier circuit of the above active EMI filter is enhanced. Since two amplifier circuits are used to inversely amplify the conducted electromagnetic interference, the voltage injection branch 7 and the current injection branch 6 are used as two feedback branches, and the total amplification gain is the sum of the amplification gains of each branch. By doing so, the gain value of the operational amplifier amplifier circuit can be reduced, while increasing the operating bandwidth of the operational amplifier. Therefore, the suppression effect on the conducted electromagnetic interference noise signal will be better, and the filtering effect on the conducted electromagnetic interference will also be improved.

[0051] Based on the above analysis of the suppression effect of conducted electromagnetic interference noise signals, simulation verification was carried out, such as Figure 2As shown, the verification process is:

[0052] S1: Confirm the structure of the dual-loop active EMI filter and model the overall circuit.

[0053] According to the dual-loop active EMI filter proposed above, the voltage detection circuit 3 adopts voltage injection, the amplification circuit uses two inverting amplification branches, the injection circuit adopts the current injection branch 6 and the voltage injection branch 7, and the LISN circuit 2 is modeled as the load of the dual-loop active EMI filter.

[0054] S2: Simplify the overall circuit model, analyze the transfer function formula, build a signal flow graph and analyze it.

[0055] The noise source is modeled as a combination of a voltage source and an impedance, the LISN circuit 2 is modeled as the load of a dual-loop active EMI filter, and the two inverting amplification branches are simplified as voltage sources to obtain a simplified overall circuit model, as shown in Figure 3 As shown, V n and Z n is the signal source and source impedance of the EMI noise source, the noise source is a signal source, and the noise impedance is an impedance used to model the signal source impedance characteristics. l is the impedance modeling of LISN circuit 2, I(s) and V l (s) represent the current and voltage on LISN circuit 2 respectively. The output signals of the two inverting amplifier branches are V c1 (s) and V c2 (s). Where R s and C s The voltage detection circuit 3 consists of the required resistors and capacitors, where R j1 and C j1 The current injection branch 6 forms the necessary resistance and capacitance. j2 The voltage injection branch 7 forms the required resistance, Z j2 is the equivalent impedance of the secondary winding side in the voltage injection branch 7. The symbol G represents the negative value of the gain of the inverting amplifier, and PE represents the protection ground.

[0056] Then analyze the transfer function from the noise source to the output of the inverting amplifier branch to the load, and build a signal flow graph model of the overall circuit model based on the transfer function results. Figure 4 As shown in the figure, R LISN and C LISN are the resistors and capacitors in LISN circuit 2. The noise source V n The voltage brought to the voltage detection circuit 3 is V sn (s), V sc1 (s) is V c1 (s) brings the voltage on the voltage detection circuit 3, Vsc2 (s) is V c2 (s) brings the voltage on the voltage detection circuit 3, V s (s) represents the final voltage on the resistor in the voltage detection circuit 3, V l (s) represents the final voltage on the resistor in LISN circuit 2. The gain of the inverting amplifier branch is represented by G 1 (s) and G 2 (s) indicates.

[0057] According to the signal flow graph model, the noise voltage V on the LISN circuit 2 before adding the active EMI filter is analyzed. 1 (s), and then analyze the noise voltage V on LISN circuit 2 after adding active EMI filter 2 (s), according to the insertion loss formula, the insertion loss expression of the active EMI filter is obtained. The insertion loss formula shows that the filtering effect of the proposed active EMI filter is improved.

[0058] V 1 is the noise signal on the load before adding the filter, which can be expressed as:

[0059]

[0060] V 2 is the noise signal on the load after adding the filter, which can be expressed as:

[0061]

[0062] The final insertion loss formula is as follows:

[0063]

[0064] It can be seen that the insertion loss of the active EMI filter is related to the loop gain of the feedback loop. The larger the loop gain, the greater the insertion loss and the better the filtering effect of the filter. Compared with the insertion loss formula of the general single-loop analog active EMI filter, it can be seen that the insertion loss formula of the dual-loop analog active EMI filter has one more item, which means that the insertion loss of the dual-loop analog active EMI filter can be greater than that of the single-loop.

[0065] Analyzing the insertion loss formula, we find that the two feedback branches have an impedance Z to the noise source. n The requirements are inconsistent. The current injection method requires Z n As large as possible, the greater the insertion loss, and the voltage injection method requires the noise source impedance Z nAs small as possible, the greater the insertion loss. For common-mode EMI noise, the noise source impedance of the actual switching power supply 8 circuit is large and fixed and cannot be changed. Therefore, it is considered to add an additional RC branch to the ground between the active EMI filter circuit and the inverter circuit. Then, the circuit analysis is carried out. The source impedance of the noise source is the parallel value of the common-mode source impedance and the RC branch. The source impedance of the noise source is very large, and the source impedance can be regarded as the impedance of the RC branch. Therefore, the noise source impedance can be adjusted according to the needs of the filter circuit.

[0066] S3: Design parameters of the dual-loop active EMI filter, including voltage detection circuit 3, amplifier circuit and injection circuit.

[0067] The parameter design of voltage detection circuit 3 needs to consider the cutoff frequency and impedance of the RC circuit. For the LSIN circuit, the values ​​of its RC circuit are 100nF and 50Ω, and the cutoff frequency is 31.8kHz. In addition, if the impedance of the RC circuit is low, a low-impedance channel from the noise source to the ground is formed, and the load impedance of the active EMI filter is reduced, affecting the operation of the active filter. Therefore, the resistance and capacitance values ​​of the voltage detection circuit 3 are designed to be 2.5nF and 2000Ω, and the cutoff frequency is 31.8kHz.

[0068] The amplifier circuit uses an inverting amplifier branch based on the operational amplifier LM7171. The design parameters considered include input resistance, feedback resistance and balance resistance. The input resistance needs to be much larger than the signal source impedance. Finally, a 10kΩ input resistance and a 150kΩ feedback resistance were selected after comprehensive consideration, and the balance resistance is the parallel value of the input resistance and the feedback resistance.

[0069] The injection circuit parameters include the current injection branch resistance, the voltage injection branch resistance, the RC branch resistance to ground and the turns ratio of the winding of the voltage injection circuit. The implementation of the active EMI filter is based on feedback compensation, and the insertion loss is actually related to the loop gain. The larger the loop gain, the greater the insertion loss. If the loop gain is K, the insertion loss is 20lg(1+K). Therefore, when analyzing the insertion loss, it is actually possible to only analyze the loop gain. When designing the injection circuit parameters, the design parameters make the loop gain as large as possible to maximize the insertion loss. It was finally determined that when the resistance of the current injection branch 6 is 50Ω, the resistance of the voltage injection circuit 7 is 10Ω, the resistance of the RC branch to ground is 24Ω and the turns ratio of the winding is 2, the insertion loss is the largest and is 20.96dB.

[0070] S4: Use Pspice circuit simulation software to build the overall circuit and simulate and verify the dual-loop active EMI filter proposed in the present invention.

[0071] The circuit simulation tool used for simulation is pspice. The simulation schematic diagram of the EMI suppression circuit is shown in Figure 5 In the figure, the parameters of the filter circuit components are listed in detail. In the dual-loop active EMI filter, the amplifier circuits in the two feedback branches are set to the same gain value, i.e. 15. Then a simulation is performed, wherein the steps include:

[0072] (1) Without adding any active EMI filter, run Pspice simulation to obtain the time domain result of the original noise. Use the FFT analysis function of Pspice to obtain the spectrum of the original noise.

[0073] (2) Add the proposed dual-loop active EMI filter and run Pspice simulation to obtain the EMI time domain results when the active EMI filter is working. Use the FFT analysis function of Pspice to obtain the EMI spectrum.

[0074] (3) Add the proposed dual-loop active EMI filter, but short-circuit the inverting amplifier input, run the Pspice simulation, and obtain the simulation time domain results of the active EMI filter not working and the passive filter working. Use the FFT analysis function of Pspice to obtain the EMI spectrum.

[0075] Figure 6 The comparison of EMI noise spectra before and after adding the filter is shown. The top curve represents the original conducted EMI spectrum without the addition of the filter circuit. The harmonics of its noise level are mainly distributed in the range of 90-100dBμV, and the noise level of some harmonics can even reach a height of more than 100dBμV. The curve in the middle shows the conducted EMI spectrum when the active EMI filter is not working, showing the passive filtering effect of the winding and the RC branch to the ground. The suppression effect on high-frequency noise is about 20dB, but the suppression effect in the low-frequency range is weak, only 9dB. The bottom curve represents the conducted EMI spectrum when the active EMI filter is working. Compared with the non-working state, the noise is effectively suppressed by about 21dB in the frequency range of 17MHz.

[0076] Figure 7 The time domain waveform comparison of the original EMI noise and before and after the filter is added is presented. The comparison shows that the passive filtering significantly reduces the peak-to-peak value of the original noise, from 10V to 1.2V. Although the change in the time domain waveform of the conducted electromagnetic interference before and after the active EMI filter is working is not obvious - this is because the operating bandwidth of the operational amplifier is limited to 16MHz - its suppression effect in the low-frequency range can be observed in the spectrum. Therefore, by combining the advantages of passive and active circuits, effective noise suppression can be achieved in a wide frequency range.

[0077] Through this simulation, the noise suppression effect of the dual-loop active EMI filter has been effectively verified. The simulation results show that the insertion loss value is about 21dB. This result fully demonstrates the effectiveness and practicality of the proposed filter design.

[0078] In summary, the analog active EMI filter with a dual-loop structure proposed in this embodiment realizes the suppression of the EMI noise of the inverter, reduces the impact on its surrounding equipment, and maintains a stable output. Compared with the general active EMI filter suppression scheme, the EMI suppression scheme of the embodiment of the present invention has a larger bandwidth and a better suppression effect on high-frequency conducted EMI. Generally, the larger the gain of the active EMI filter amplifier circuit, the greater the insertion loss and the better the filtering effect. However, in actual implementation, the larger the gain design of the amplifier circuit based on the operational amplifier, the lower its effective bandwidth will be, which will affect the bandwidth of the active circuit. The embodiment of the present invention uses a dual-loop structure to use two inverting amplifier branches to invert the conducted electromagnetic interference, and the total amplification gain of the two feedback branches is the sum of the amplification gains of each branch. By doing so, the gain value of the operational amplifier amplifier circuit can be reduced, while increasing the operating bandwidth of the operational amplifier, thereby improving the performance of the active EMI filter. This embodiment can be used for the suppression of conducted electromagnetic interference at the DC input end of the DC-AC inverter, and can also be used for the suppression of conducted EMI of the DC-DC converter. The insertion loss formula finally obtained by the EMI suppression scheme of the present invention is related to the loop gain of the feedback loop. The larger the loop gain, the larger the insertion loss and the better the filtering effect of the filter. Compared with the insertion loss formula of the general active EMI filter, the insertion loss formula of the dual-loop active EMI filter proposed by the present invention has one more term and a larger insertion loss. Since two inverting amplifiers are used to amplify the signal, the gain setting of the inverting amplifier can be reduced and the bandwidth can be increased. Therefore, the active EMI filter proposed by the present invention is better than the general active EMI filter in suppressing high-frequency EMI.

[0079] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0080] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. An analog active EMI filter with a dual-loop structure, characterized in that: The invention comprises a direct current power supply (1), a LISN circuit (2), a voltage detection circuit (3), an injection circuit, an amplifier circuit and a switching power supply (8); the direct current power supply (1), the LISN circuit (2), the voltage detection circuit (3), the injection circuit and the switching power supply (8) are connected in parallel in sequence; the injection circuit comprises a voltage injection branch (7) and a current injection branch (6) connected in parallel therewith, which are used for voltage injection and current injection respectively; the amplifier circuit comprises a first inverting amplifier branch (4) and a second inverting amplifier branch (5) connected in parallel therewith; the first inverting amplifier branch (4) is connected to the voltage detection circuit (3) and the current injection branch (6) respectively to form a first ring structure; the second inverting amplifier branch (5) is connected to the voltage detection circuit (3) and the voltage injection branch (7) respectively to form a second ring structure.

2. The dual-loop structure analog active EMI filter according to claim 1, characterized in that: The voltage detection circuit (3) uses a first-order RC high-pass circuit to realize voltage detection. The first-order RC high-pass circuit comprises a resistor and a capacitor connected thereto.

3. The dual-loop structure analog active EMI filter according to claim 1, characterized in that: The current injection branch (6) adopts an RC circuit, which includes a resistor and a capacitor connected thereto, and the voltage injection branch (7) includes a resistor and three windings connected thereto.

4. The dual-loop structure analog active EMI filter according to claim 1, characterized in that: The first inverting amplifier branch (4) and the second inverting amplifier branch (5) are both constructed based on operational amplifiers and are used to amplify and output the EMI noise source.

5. The dual-loop structure analog active EMI filter according to claim 1, characterized in that: The first inverting amplifying branch (4) and the second inverting amplifying branch (5) both comprise an operational amplifier, an input resistor, a feedback resistor and a grounding resistor, wherein the input resistor is connected to the inverting input terminal of the operational amplifier, the feedback resistor is connected between the output terminal and the inverting input terminal of the operational amplifier, and the grounding resistor is connected to the inverting input terminal of the operational amplifier.

6. A noise suppression verification method for an analog active EMI filter with a dual-ring structure according to any one of claims 1 to 5, characterized in that: The following steps are involved: The analog active EMI filter of the dual-loop structure is modeled as a whole and simplified to obtain a simplified overall circuit model; Based on the simplified overall circuit model, the transfer function from the EMI noise source and the output of the amplifier circuit to the LISN circuit (2) is analyzed to build a signal flow graph model; According to the signal flow graph model, design parameters of the analog active EMI filter of the dual-loop structure; The simulation verification is carried out according to the designed parameters to obtain the verification results.

7. The noise suppression verification method according to claim 6, characterized in that: The step of obtaining a simplified overall circuit model comprises: Based on the overall modeled dual-loop structure analog active EMI filter, the noise source is modeled as a noise voltage source and a source impedance, and the first inverting amplifier branch (4) and the second inverting amplifier branch (5) connected in parallel therewith are simplified as compensation voltage sources, thereby obtaining the simplified overall circuit model.

8. The noise suppression verification method according to claim 6, characterized in that: The parameter design steps include: According to the cut-off frequency and impedance of the first-order RC high-pass circuit and the RC circuit, the cut-off frequency and resistance and capacitance values ​​of the voltage detection circuit (3) are designed; According to the resistance value of the noise source impedance, design the parameters of the amplifier circuit, including input resistance, feedback resistance and balancing resistance; Analyzing the relationship between the insertion loss and the loop gain of the injection circuit according to the signal flow graph model; According to the relationship between the insertion loss and the loop gain of the injection circuit, the parameters of the injection circuit are designed to maximize the insertion loss.

9. The noise suppression verification method according to claim 8, characterized in that: The insertion loss formula is: in: Where IL is, V1(s) is the noise voltage on the LISN circuit (2) before adding the EMI filter, V2(s) is the noise voltage on the LISN circuit (2) after adding the EMI filter, G1(s) and G2(s) are the gains of the second inverting amplifier branch (5) and the first inverting amplifier branch (4), and Z is n is the source impedance, Z j2 The impedance on the primary side of the three windings is expressed as the equivalent resistance on the secondary side, Z l is the impedance of the LISN circuit (2), R s , C s are the resistance and capacitance in the first-order RC high-pass circuit, V n (s) is the noise source, R LISN , C LISN are the resistance and capacitance of the LISN circuit (2).

10. The noise suppression verification method according to claim 6, characterized in that: The simulation process includes: Without obtaining any analog active EMI filter for simulation, the spectrum of the original noise source is obtained; Acquire the simulated active EMI filter of the dual-ring structure for simulation, and obtain the spectrum of the EMI noise source when the simulated active EMI filter of the dual-ring structure is working; The simulated active EMI filter of the dual-ring structure is obtained, and its amplifying circuit input is short-circuited and then simulated to obtain the spectrum of the EMI noise source when the simulated active EMI filter of the dual-ring structure is not working.

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