Full-band compact hybrid emi filter circuit design method based on current feedback

Abstract

This invention proposes a design method for a full-band compact hybrid EMI filter circuit based on current feedback. The method includes: constructing an electromagnetic interference test circuit to obtain the common-mode EMI spectrum required for attenuation by the PWM converter, and establishing a high-frequency equivalent circuit for the PWM converter; obtaining the optimal hybrid EMI filter topology based on the high-frequency equivalent models of active and passive EMI filter circuits and the noise attenuation characteristics of the hybrid EMI filter circuit topology; designing the active EMI filter topology and its high-frequency equivalent model based on the noise cancellation principle of the active EMI filter and the common-mode EMI spectrum; designing the active EMI filter topology based on the noise cancellation principle of the active EMI filter and the common-mode EMI spectrum; designing the passive EMI filter structure based on the common-mode EMI noise spectrum after adding the active EMI filter; and designing the hybrid EMI filter circuit based on the hybrid EMI filter topology, the active EMI filter topology, the passive EMI filter structure, and the high-frequency equivalent models of the active and passive EMI filter circuits.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a full-band compact hybrid EMI filter circuit based on current feedback. Background Technology

[0002] With the widespread use of wide-bandgap semiconductors, the switching frequencies of switching devices are constantly increasing, and the serious problem of electromagnetic interference (EMI) has attracted widespread attention. Among these issues, significant common-mode conducted radiation caused by the parasitic capacitance of switching devices and heat sinks is a key factor in EMI generation by power converters. To prevent this from affecting the normal operation of the converter itself and other equipment, and to ensure stable operation, a common-mode EMI filter is generally required. The addition of a common-mode EMI filter composed of passive capacitors and inductors increases the size and weight of the device and reduces power density; while active EMI filters, due to their small size and high integration, have broad application prospects in power electronic converters.

[0003] However, compared to traditional passive EMI filters, active EMI filters are not as widely used in practical engineering. The main reason is that active components are affected by the gain-bandwidth product, resulting in a often lower effective bandwidth. Furthermore, in the detection stage, traditional active EMI filters use large magnetic cores for common-mode current acquisition, which doesn't significantly reduce the overall size compared to passive EMI filters. In addition, the performance of any active EMI filter topology containing a magnetic core depends on the parameters of the transformer core. Temperature, operating current, and magnetic field coupling will degrade transformer performance, leading to a decrease in the overall attenuation performance of the EMI filter. Therefore, a single filter type, due to its inherent limitations, will find it difficult to meet the required filtering requirements.

[0004] Hybrid filtering has become an important tool for dealing with harsh electromagnetic interference environments. It combines the advantages of various filtering methods with complementary ideas to attenuate electromagnetic noise across the entire conducted frequency band. However, due to the influence of size, hybrid EMI filters are not conducive to improving the power density of PWM converters. In addition, due to the complex structure of hybrid EMI filters, it is difficult to model them and quantify the filtering effect of different topologies, and it is also difficult to form a standardized design process. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the related art.

[0006] Therefore, the purpose of this invention is to propose a design method for a full-band compact hybrid EMI filter circuit based on current feedback, which describes the filtering effect and design method of EMI filters and is easy to operate and implement.

[0007] To achieve the above objectives, a first aspect of the present invention proposes a design method for a full-band compact hybrid EMI filter circuit based on current feedback, comprising:

[0008] Based on a linear stable impedance network, an electromagnetic interference test circuit was built to obtain the common-mode EMI spectrum required for attenuation of the PWM converter, and a high-frequency equivalent circuit of the PWM converter was established.

[0009] Based on the high-frequency equivalent circuit of the PWM converter, high-frequency equivalent models of active and passive EMI filter circuits are constructed. According to the high-frequency equivalent models of active and passive EMI filter circuits and the noise attenuation characteristics of the hybrid EMI filter circuit topology, the optimal hybrid EMI filter topology is obtained.

[0010] Based on the noise cancellation principle of the active EMI filter and the common-mode EMI spectrum, an active EMI filter topology is designed; based on the common-mode EMI noise spectrum after adding the active EMI filter, a passive EMI filter structure is designed.

[0011] The hybrid EMI filter circuit is designed based on the hybrid EMI filter topology, the active EMI filter topology, the passive EMI filter structure, and the high-frequency equivalent model of the active and passive EMI filter circuits.

[0012] In addition, the full-band compact hybrid EMI filter circuit design method based on current feedback according to the above embodiments of the present invention may also have the following additional technical features:

[0013] Furthermore, in one embodiment of the present invention, the circuit may include an active EMI filter circuit and a passive EMI filter circuit, wherein,

[0014] The active EMI filter circuit consists of a frequency-selective network, a phase compensator, an amplification network, and a passive injection network, and is used to attenuate the noise amplitude within the inherent bandwidth of the active network.

[0015] The passive EMI filter circuit consists of a common-mode inductor and a grounding capacitor, and is used to attenuate the amplitude of high-frequency noise that is not attenuated by the active EMI filter circuit.

[0016] Furthermore, in one embodiment of the present invention, obtaining the optimal hybrid EMI filter topology based on the equivalent models of the active and passive EMI filters and the noise attenuation characteristics of different hybrid EMI filter topologies includes:

[0017] Based on different combinations of the active and passive EMI filter circuits, the hybrid EMI filter topology can be divided into two combinations: passive EMI filter near the interference source and active EMI filter near the interference source. An equivalent circuit model is drawn based on the common-mode noise conduction loop, and an insertion loss expression describing the filtering effect is obtained. The insertion losses for the two combinations are as follows:

[0018]

[0019] ,

[0020] Wherein, IL1 is the insertion loss model of the passive EMI filter when it is close to the interference source, IL2 is the insertion loss model of the active EMI filter when it is close to the interference source, and V L1 V represents the common-mode voltage across the equivalent impedance of the linearly stable impedance network without an EMI filter. L2 Z is the common-mode voltage across the equivalent impedance of the LISN terminal after adding an EMI filter. s and Z L These are the equivalent impedances of the common-mode interference source and the LISN terminal, respectively. Lcm and Z cy These are the common-mode inductance and grounding capacitance values ​​of the passive EMI filter, respectively. i is the current amplification factor of the equivalent controlled source model of the active EMI filter;

[0021] Subtracting the insertion loss expressions for the different models yields the expression describing the difference in filtering performance:

[0022] .

[0023] Furthermore, in one embodiment of the present invention, the insertion loss expression and closed-loop transfer function of the active EMI filter are obtained based on the high-frequency equivalent model of the active EMI filter:

[0024]

[0025]

[0026] Among them, V L V' is the common-mode voltage across the equivalent impedance of the linearly stable impedance network without an EMI filter. L To determine the common-mode voltage across the equivalent impedance of the linearly stable impedance network after adding an EMI filter, I L Z is the current flowing into the equivalent impedance of the linear stable impedance network. S Z is the noise source impedance of the common-mode interference source. L T is the equivalent impedance value of a linear stable impedance network.comp (s) is the transfer function of the system's phase compensator, G b (s) is the closed-loop transfer function of the op-amp, and s is the Laplace variable.

[0027] Furthermore, in one embodiment of the present invention, the design of passive EMI filter circuit parameters is performed based on the common-mode EMI spectrum when the active EMI filter circuit is installed, the insertion loss of the active EMI filter circuit, and the passive EMI filter structure, including:

[0028] The common-mode inductance L of the passive EMI filter circuit without the active EMI filter is calculated using the following formula. eq1 The common-mode inductor L of the passive EMI filter circuit when the active EMI filter is added. eq2 Inductance ratio:

[0029]

[0030] Among them, the point at which the insertion loss curve of the passive EMI filter first becomes tangent to the common-mode EMI noise spectrum to be attenuated before the active EMI filter is installed is a(f a M a The point at which the common-mode EMI noise spectrum, before and after the installation of the active EMI filter, first becomes tangent to the desired attenuation is b(f). b M b ), ΔM is the difference between the excessive EMI spectrum without the active EMI filter and with the active EMI filter installed, C eq1 and C eq2 These represent the Y-capacitance values ​​of the passive EMI filter without the active EMI filter and the Y-capacitance values ​​of the passive EMI filter with the active EMI filter installed, respectively.

[0031] The parameters of the passive EMI filter circuit are designed based on the inductance ratio.

[0032] Furthermore, in one embodiment of the present invention, the hybrid EMI filter circuit is designed based on the hybrid EMI filter topology, the active EMI filter topology and parameters, and the passive EMI filter structure and parameters, wherein the insertion loss expression of the hybrid EMI filter is:

[0033]

[0034] Among them, I L I represents the common-mode current across the equivalent impedance of the linearly stable impedance network without an EMI filter. LtG(s) represents the common-mode current across the equivalent impedance of the linearly stable impedance network after the EMI filter is added, and Z represents the closed-loop transfer function of the active EMI filter. Cy Z represents the impedance value of the Y capacitor in the passive EMI filter. Lc Z represents the impedance value of the common-mode inductor in the passive EMI filter. L Let be the equivalent impedance of the linear stable impedance network, and s be the Laplace variable.

[0035] Furthermore, in one embodiment of the present invention, the hybrid EMI filter circuit is applicable to all PWM converters, and the design method is applicable to the suppression of conducted common-mode and differential-mode EMI.

[0036] This invention proposes a full-bandwidth compact hybrid EMI filter circuit design method based on current feedback. It leverages the advantages of active EMI filters in suppressing low-frequency noise and passive EMI filters in suppressing high-frequency noise, combining active and passive EMI filters. The common-mode EMI loop of the PWM converter is obtained using high-frequency equivalent circuit modeling. The active EMI filter topology is designed based on the noise cancellation principle of the active EMI filter. Then, the parameters of the active EMI filter are set according to the required attenuation EMI spectrum, and its transfer function is derived. Based on the common-mode EMI noise spectrum after adding the active EMI filter, the structure and parameters of the passive EMI filter are designed. Finally, the transfer function of the entire hybrid EMI filter is derived and modeled, thus accurately describing the noise attenuation effect and effective bandwidth of the hybrid EMI filter.

[0037] The current feedback-based full-band compact hybrid EMI filter design method of this invention combines the design of active EMI filters and passive EMI filters. By combining the advantages of each, it achieves the goal of attenuating conducted noise across the entire frequency band and further reduces the size of the EMI filter. Optimal topology selection for the hybrid EMI filter is achieved through modular and precise modeling, and small-volume surface-mount components replace the large-volume isolation transformers in traditional active EMI filters. This complementary approach optimizes the EMI filter's filtering effect and minimizes its size, providing a complete design guide for hybrid EMI filters. Attached Figure Description

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0039] Figure 1 This is a flowchart of a full-band compact hybrid EMI filter circuit design method based on current feedback according to an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the common-mode EMI test circuit of the Boost converter topology and linear stable impedance network according to an embodiment of the present invention;

[0041] Figure 3 The measured common-mode EMI spectrum of a Boost converter under conventional fixed-frequency PWM according to an embodiment of the present invention;

[0042] Figure 4 This is a schematic diagram of the topology of a passive EMI filter in a hybrid EMI filter according to an embodiment of the present invention;

[0043] Figure 5 This is a schematic diagram of the equivalent circuit of the passive EMI filter near the interference source in the hybrid EMI filter according to an embodiment of the present invention;

[0044] Figure 6 A schematic diagram of the equivalent circuit of an active EMI filter in a hybrid EMI filter near an interference source according to an embodiment of the present invention;

[0045] Figure 7 Insertion loss curves for different hybrid EMI filter combination topologies according to embodiments of the present invention;

[0046] Figure 8 This is a design flowchart of a hybrid EMI filter according to an embodiment of the present invention;

[0047] Figure 9 This is a schematic diagram of a full-band compact hybrid EMI filter topology and test circuit applicable to PWM converters according to an embodiment of the present invention;

[0048] Figure 10 This is a frequency response curve of the noise detection frequency selection network in an active EMI filter according to an embodiment of the present invention.

[0049] Figure 11 This is a schematic diagram of the amplifier circuit topology in an active EMI filter according to an embodiment of the present invention;

[0050] Figure 12 This is a comparison diagram of the phase angle characteristic curves before and after adding a phase angle compensator to an active EMI filter according to an embodiment of the present invention;

[0051] Figure 13 This is a signal flow diagram of the transfer functions of each module in an active EMI filter according to an embodiment of the present invention.

[0052] Figure 14 This is a comparison diagram of the common-mode EMI spectrum of the Boost converter before and after adding an active EMI filter according to an embodiment of the present invention.

[0053] Figure 15This is a schematic diagram of the common-mode equivalent path of a Boost converter after adding a hybrid EMI filter according to an embodiment of the present invention.

[0054] Figure 16 This is a common-mode signal flow diagram of a Boost converter after adding a hybrid EMI filter according to an embodiment of the present invention.

[0055] Figure 17 This is a schematic diagram comparing the insertion loss of a hybrid EMI filter and an LC-type passive EMI filter according to an embodiment of the present invention.

[0056] Figure 18 The common-mode EMI spectrum of the Boost converter after adding a hybrid EMI filter according to an embodiment of the present invention. Detailed Implementation

[0057] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0058] The following describes, with reference to the accompanying drawings, a design method for a full-band compact hybrid EMI filter circuit based on current feedback according to an embodiment of the present invention.

[0059] Figure 1 This is a flowchart illustrating a design method for a full-band compact hybrid EMI filter circuit based on current feedback, provided in an embodiment of the present invention.

[0060] like Figure 1 As shown, the design method for a full-band compact hybrid EMI filter circuit based on current feedback includes the following steps:

[0061] S101: Based on a linear stable impedance network, an electromagnetic interference test circuit is built to obtain the common-mode EMI spectrum required for attenuation of the PWM converter, and a high-frequency equivalent circuit of the PWM converter is established.

[0062] Furthermore, in one embodiment of the present invention, the circuit may include an active EMI filter circuit and a passive EMI filter circuit, wherein,

[0063] The active EMI filter circuit consists of a frequency-selective network, a phase compensator, an amplification network, and a passive injection network, and is used to attenuate the noise amplitude within the inherent bandwidth of the active network.

[0064] The passive EMI filter circuit consists of a common-mode inductor and a grounding capacitor, and is used to attenuate the amplitude of high-frequency noise that is not attenuated by the active EMI filter circuit.

[0065] In step S101, the common-mode EMI spectrum required for the Boost converter to be attenuated is obtained by testing with a linear stable impedance network.

[0066] Furthermore, the common-mode EMI spectrum required for attenuation of the PWM converter is obtained through the linear stable impedance network, as shown in the test diagram. Figure 2 As shown, this includes: using the linear stable impedance network for common-mode EMI, and designing margins according to electromagnetic compatibility standards to obtain the desired attenuation of the common-mode EMI spectrum.

[0067] The operating circuit parameters of the Boost converter are shown in the table below:

[0068] parameter numerical values parameter numerical values <![CDATA[Input voltage V dc > 48V <![CDATA[Input capacitor C X1 > 22uF <![CDATA[Output voltage V out > 110V <![CDATA[Output capacitor C out > 100uF <![CDATA[Switching frequency F r > 100kHz <![CDATA[Inductance L b > 200uH <![CDATA[Load resistance R L > 700Ω

[0069] The common-mode EMI voltage and current are obtained by the following formula:

[0070]

[0071] I CM =i N +i L

[0072] Among them, v N It is the voltage value measured on line N in a linear stable impedance network, v L It is the voltage value measured on line L in a linear stable impedance network, i N This is the current value measured on line N in LISN, i L It is the current value measured on line L in LISN.

[0073] Furthermore, such as Figure 3 The image shows the common-mode EMI spectrum of the PWM converter obtained by testing with a linear stable impedance network in an embodiment of the present invention. Figure 4 The diagram shows the topology of the passive EMI filter. The point of first tangency between the filter and the spectrum is recorded as a(f). a M a The slope SdB / dec of the filter insertion loss curve, and the intersection point of the insertion loss curve with the frequency axis when the tangent point is extended in the opposite direction (f). c1 The common-mode inductance value L when only a passive EMI filter is added can be calculated using the following formula (0). eq1 :

[0074]

[0075] Where L c1 C is the common-mode inductor in a passive EMI filter. y1 This refers to the capacitance to ground in a passive EMI filter.

[0076] S102: Based on the high-frequency equivalent circuit of the PWM converter, construct high-frequency equivalent models of active and passive EMI filter circuits. According to the high-frequency equivalent models of the active and passive EMI filter circuits and the noise attenuation characteristics of the hybrid EMI filter circuit topology, obtain the optimal hybrid EMI filter topology.

[0077] Furthermore, in one embodiment of the present invention, obtaining the optimal hybrid EMI filter topology based on the equivalent models of the active and passive EMI filters and the noise attenuation characteristics of different hybrid EMI filter topologies includes:

[0078] Based on different combinations of the active and passive EMI filter circuits, the hybrid EMI filter topology can be divided into two combinations: passive EMI filter near the interference source and active EMI filter near the interference source. An equivalent circuit model is drawn based on the common-mode noise conduction loop, and an insertion loss expression describing the filtering effect is obtained. The insertion losses for the two combinations are as follows:

[0079]

[0080] ,

[0081] Wherein, IL1 is the insertion loss model of the passive EMI filter when it is close to the interference source, IL2 is the insertion loss model of the active EMI filter when it is close to the interference source, and V L1 V represents the common-mode voltage across the equivalent impedance of the linearly stable impedance network without an EMI filter. L2 Z is the common-mode voltage across the equivalent impedance of the LISN terminal after adding an EMI filter. s and Z L These are the equivalent impedances of the common-mode interference source and the LISN terminal, respectively. Lcm and Z cy These are the common-mode inductance and grounding capacitance values ​​of the passive EMI filter, respectively. i is the current amplification factor of the equivalent controlled source model of the active EMI filter;

[0082] Subtracting the insertion loss expressions for the different models yields the expression describing the difference in filtering performance:

[0083] .

[0084] Furthermore, the active EMI filter circuit consists of a frequency selection network, a phase compensator, an amplification network, and a passive injection network, and is used to attenuate the noise amplitude within the inherent bandwidth of the active network.

[0085] Among them, the first-order high-pass frequency selection network of the noise detection section is composed of C s1 and R s1 The circuit is configured such that it is isolated from the main circuit by a voltage follower formed by operational amplifier 1; the amplification network consists of a feedback loop formed by operational amplifier 2 and a push-pull amplifier, with the feedback resistor R of the operational amplifier being... a2 With the subsequent passive injection network R in and C in Connect the midpoints directly to the op-amp input resistor R. a1 Connected to the preamplifier phase angle compensator; the push-pull amplifier input is directly connected to the OPAM output; the second-order phase angle compensation stage is composed of R c1 R c2 and C c1 This is designed to compensate for the significant phase angle shift caused by passive components.

[0086] Furthermore, in one embodiment of the present invention, the insertion loss expression and closed-loop transfer function of the active EMI filter are obtained based on the high-frequency equivalent model of the active EMI filter:

[0087]

[0088]

[0089] Among them, V L V' is the common-mode voltage across the equivalent impedance of the linearly stable impedance network without an EMI filter. L To determine the common-mode voltage across the equivalent impedance of the linearly stable impedance network after adding an EMI filter, I L Z is the current flowing into the equivalent impedance of the linear stable impedance network. S Z is the noise source impedance of the common-mode interference source. L T is the equivalent impedance value of a linear stable impedance network. comp (s) is the transfer function of the system's phase compensator, G b (s) is the closed-loop transfer function of the op-amp, and s is the Laplace variable.

[0090] In step S102, based on the equivalent models of active and passive EMI filters and different topological combinations of hybrid EMI filters, the following can be obtained: Figure 5-6 The diagram shows different topology combinations of hybrid EMI filters. These topology combinations are categorized into passive EMI filters positioned near the interference source and active EMI filters positioned near the interference source.

[0091] As defined by insertion loss, a passive EMI filter achieves its best filtering effect when close to the interference source. To describe the spectral performance of insertion loss, a set of test values ​​can be used for simulation. The test data table is as follows:

[0092] Specific parameters Variable representation Test value Controlled source current amplification factor <![CDATA[B i ]]> 20 Passive EMI filter grounding capacitor <![CDATA[C y ]]> 2200pF Passive EMI filter common mode inductor <![CDATA[L cm ]]> 1mH LISN equivalent resistance <![CDATA[Z L ]]> 25Ω

[0093] It is understandable that, such as Figure 7 As shown, the passive EMI filter has better high-frequency performance when it is close to the interference source, that is, the effective attenuation bandwidth of the passive EMI filter is wider when it is close to the interference source. The optimal selection of the hybrid EMI filter topology can be obtained through the above method.

[0094] S103: Based on the noise cancellation principle of the active EMI filter and the common-mode EMI spectrum, design the active EMI filter topology; based on the common-mode EMI noise spectrum after adding the active EMI filter, design the passive EMI filter structure.

[0095] Furthermore, in one embodiment of the present invention, the design of passive EMI filter circuit parameters is performed based on the common-mode EMI spectrum when the active EMI filter circuit is installed, the insertion loss of the active EMI filter circuit, and the passive EMI filter structure, including:

[0096] The common-mode inductance L of the passive EMI filter circuit without the active EMI filter is calculated using the following formula. eq1 The common-mode inductor L of the passive EMI filter circuit when the active EMI filter is added. eq2 Inductance ratio:

[0097]

[0098] Among them, the point at which the insertion loss curve of the passive EMI filter first becomes tangent to the common-mode EMI noise spectrum to be attenuated before the active EMI filter is installed is a(f a M a The point at which the common-mode EMI noise spectrum, before and after the installation of the active EMI filter, first becomes tangent to the desired attenuation is b(f). b M b ), ΔM is the difference between the excessive EMI spectrum without the active EMI filter and with the active EMI filter installed, C eq1 and C eq2 These represent the Y-capacitance values ​​of the passive EMI filter without the active EMI filter and the Y-capacitance values ​​of the passive EMI filter with the active EMI filter installed, respectively.

[0099] The parameters of the passive EMI filter circuit are designed based on the inductance ratio.

[0100] In step S103, based on the effective attenuation bandwidth and characteristics of the active EMI filter and the passive EMI filter, the following is planned: Figure 8The design process of the hybrid EMI filter shown is as follows: First, the topology and parameters of the active EMI filter are designed based on the noise cancellation principle of the active EMI filter, and the transfer function model of the active EMI filter is established. Finally, the topology and parameters of the passive EMI filter are designed based on the common-mode EMI spectrum that needs to be attenuated after adding the active EMI filter.

[0101] Specifically, the overall topology of the full-band compact hybrid EMI filter circuit based on current feedback is as follows: Figure 9 As shown, the active EMI filter topology consists of five parts: a noise selective network, a phase compensator, an amplification network, and a passive injection network.

[0102] Furthermore, by analyzing the characteristics of the common-mode noise interference source, the cutoff frequency of the high-pass filter in the detection stage is set near the common-mode noise frequency.

[0103] The frequency response curve of the transfer function of the noise detection circuit used in this embodiment of the invention is as follows: Figure 10 As shown, filtering out irrelevant low-frequency voltages through a high-pass filter can prevent saturation of the operational amplifier in the subsequent amplifier circuit and prevent high-frequency noise above the switching frequency from entering the next stage circuit.

[0104] The common-mode noise voltage is sampled, and the acquired voltage signal is amplified by an operational amplifier and then by a power amplifier. Finally, it is injected through capacitor C. in Injected into ground. The amplifier circuit, for example... Figure 11 As shown, the preamplifier stage is a voltage amplifier circuit composed of operational amplifiers, and the post-amplifier stage is a push-pull circuit that enhances the current output capability of the active EMI filter.

[0105] Furthermore, by establishing a transfer function model of the active EMI filter, the phase angle characteristic curve of the active EMI filter can be calculated, such as... Figure 12 As shown, after phase compensation by the phase angle compensator, the injected current of the active EMI filter will be in phase with the noise current, which satisfies the principle and requirements of noise cancellation of the active EMI filter.

[0106] Furthermore, by establishing transfer function models for each module, it is possible to establish, for example... Figure 13 The transfer function block diagram of the active EMI filter topology is shown, where I s I represents the common-mode current of the noise source. L I represents the sum of the currents through the detection resistor on the LISN. cancel The compensation current is used to indicate that the active EMI filter will have the best noise cancellation effect when the compensation current can meet the requirements of the current of the sensing resistor on the LISN and the same frequency, phase and amplitude.

[0107] Specifically, the common-mode EMI spectrum comparison chart with and without active EMI filters is shown below. Figure 14 As shown, the amplitude difference between the two in the lower frequency band is about 20 dBμV. In the mid-frequency band around 1 MHz, the EMI amplitude after adding an active EMI filter is about 30 dBμV lower than that without it. This indicates that adding an active EMI filter can effectively reduce the peak EMI spectrum in the low and mid-frequency bands. However, in the high-frequency range above 10 MHz, the noise attenuation effect of the operational amplifier in the active EMI filter is no longer significant due to the limitation of the gain-bandwidth product. Therefore, it is necessary to combine a passive EMI filter with an active EMI filter for high-frequency noise attenuation.

[0108] Based on the common-mode EMI spectrum obtained from the test with the active EMI filter installed, this embodiment of the invention can calculate the required common-mode inductance value at the point where the insertion loss curve of the passive EMI filter is first tangent to the common-mode EMI spectrum to be attenuated. At the tangent point, the difference in EMI spectrum between the active EMI filter installed and the uninstalled active EMI filter is recorded as ΔM, and the cutoff frequency after installing the active EMI filter is set to f. c2 The coordinates of the point of tangency are b(f) b M b Based on the relationship between the cutoff frequency and the cutoff frequency of the LC-type passive EMI filter, the common-mode inductance L without the active EMI filter can be calculated using the following formula. c1 The common-mode inductor L when the active EMI filter is added c2 Inductance ratio:

[0109]

[0110] Where C y1 and C y2 These represent the Y capacitance values ​​without and with the active EMI filter, respectively. The greater the difference in the cutoff frequency and amplitude between the active EMI filter and the unactive filter, the greater the decrease in inductance and the more significant the reduction in size. Therefore, using a hybrid EMI filter can reduce the overall EMI filter size while balancing high-frequency and low-frequency noise, thereby improving the power density of the PWM converter.

[0111] Based on the hybrid EMI filter topology, a compact hybrid EMI filter transfer function model is established. The insertion loss expression of the hybrid filter is calculated based on the hybrid EMI filter transfer function model, and the noise attenuation effect of the hybrid EMI filter is quantified and evaluated.

[0112] S104: Design the hybrid EMI filter circuit based on the hybrid EMI filter topology, the active EMI filter topology, the passive EMI filter structure, and the high-frequency equivalent model of the active and passive EMI filter circuits.

[0113] Step S104 further includes measuring the filtered common-mode EMI spectrum based on the hybrid EMI filter topology and the Boost common-mode noise test circuit.

[0114] Furthermore, such as Figure 15 As shown, an equivalent common-mode noise circuit for the PWM converter after adding a hybrid EMI filter is established, and a circuit is established as follows: Figure 16 The block diagram of the transfer function model of the hybrid EMI filter shown is shown, where I s I represents the common-mode current of the noise source. st I represents the noise current after passing through the passive EMI filter. Lt I represents the sum of the currents through the detection resistor on the LISN. AEF This indicates the compensation current.

[0115] It is understood that the insertion loss expression of the hybrid EMI filter can be obtained from the feedback control block diagram of the active EMI filter and the passive EMI filter, wherein the insertion loss expression of the hybrid EMI filter is:

[0116]

[0117] Among them, I L I represents the common-mode current across the equivalent impedance of the linearly stable impedance network without an EMI filter. Lt G(s) represents the common-mode current across the equivalent impedance of the linearly stable impedance network after the EMI filter is added, and Z represents the closed-loop transfer function of the active EMI filter. Cy Z represents the impedance value of the Y capacitor in the passive EMI filter. Lc Z represents the impedance value of the common-mode inductor in the passive EMI filter. L Let be the equivalent impedance of the linear stable impedance network, and s be the Laplace variable.

[0118] Specifically, by deriving the insertion loss expression for the compact hybrid EMI filter, the following can be directly obtained: Figure 17 The diagram shows the insertion loss frequency characteristics. Comparing the insertion loss of a single passive EMI filter and a hybrid EMI filter, it can be seen that the hybrid EMI filter compensates for the low-frequency deficiency of a single passive EMI filter, and also supplements the effective bandwidth of the active EMI filter. In addition, since the active EMI filters are all surface-mount devices, they do not affect the overall size of the EMI filter.

[0119] Furthermore, in one embodiment of the present invention, the hybrid EMI filter circuit is designed based on the hybrid EMI filter topology, the active EMI filter topology and parameters, and the passive EMI filter structure and parameters, wherein the insertion loss expression of the hybrid EMI filter is:

[0120] ,

[0121] Among them, I L I represents the common-mode current across the equivalent impedance of the linearly stable impedance network without an EMI filter. Lt G(s) represents the common-mode current across the equivalent impedance of the linearly stable impedance network after the EMI filter is added, and Z represents the closed-loop transfer function of the active EMI filter. Cy Z represents the impedance value of the Y capacitor in the passive EMI filter. Lc Z represents the impedance value of the common-mode inductor in the passive EMI filter. L Let be the equivalent impedance of the linear stable impedance network, and s be the Laplace variable.

[0122] Furthermore, such as Figure 18 As shown, within the conducted common-mode noise measurement spectrum range of 150kHz-30MHz, the common-mode noise of the experimentally measured PWM converter decreased to below the CISPR 22 electromagnetic compatibility standard limit. Because the hybrid EMI filter combines the advantages of both active and passive EMI filters, it achieves noise attenuation across the entire frequency range. Furthermore, the presence of the active EMI filter increases the cutoff frequency of the passive EMI filter, thereby reducing the common-mode inductance and ultimately decreasing the overall size of the PWM converter.

[0123] Specifically, common-mode noise testing was conducted on the PWM converter using a circuit platform. To test the optimization effect and size of the hybrid EMI filter, the changes in the volume and inductance of the common-mode inductor were tested and compared with those of a single passive EMI filter and the hybrid EMI filter under the same effect, with the limit being just below the CISPR22 electromagnetic interference standard. The test results are shown in the table below:

[0124]

[0125]

[0126] Understandably, the hybrid EMI filter adds an active EMI filter. Since active EMI filters are all composed of surface-mount components, they can be integrated. Therefore, it can be assumed that the common-mode inductor still dominates the size of the hybrid EMI filter. As the above analysis shows, this compact hybrid EMI filter significantly reduces the size of the common-mode inductor while ensuring full-band common-mode noise suppression, thereby improving the power density of the PWM converter.

[0127] Furthermore, in one embodiment of the present invention, the hybrid EMI filter circuit is applicable to all PWM converters, and the design method is applicable to the suppression of conducted common-mode and differential-mode EMI.

[0128] Technical Effects of this Application: In one embodiment of this application, the present invention further combines the design of active EMI filters and passive EMI filters in a PWM converter. It leverages the advantage of active EMI filters in low-frequency noise attenuation, overcoming the problem of low power density caused by using large-volume common-mode inductors to attenuate common-mode noise. Furthermore, by analyzing the equivalent circuit model of the hybrid EMI filter, an optimal topology selection method for the hybrid EMI filter is obtained. Based on the active EMI filter design method, a transformerless active EMI filter topology is established, further reducing the size of the active EMI filter. Simultaneously, the transfer function models of each module of the active EMI filter are analyzed in detail, further quantifying the attenuation effect and effective bandwidth of the active EMI filter. The parameters of the passive EMI filter can be designed using the common-mode EMI noise spectrum after attenuation by the active EMI filter. By coordinating the two, the active EMI filter primarily attenuates noise in the low-frequency range, while the passive EMI filter attenuates noise in the high-frequency range, thereby achieving attenuation of noise across the entire frequency range and optimizing the overall size.

[0129] Technical advantages of this application: The compact hybrid EMI filter circuit based on current feedback across the entire frequency band disclosed in this application is the result of extensive research conducted by the applicant. It can reduce the amplitude of EMI across the entire conducted frequency band and significantly reduce the overall size of the EMI filter. In other words, this application is a specific solution obtained by the applicant through extensive creative work.

[0130] The current feedback-based full-band compact hybrid EMI filter design method proposed in this invention, compared with traditional passive EMI filters, attenuates noise in the low-frequency band due to the presence of active EMI filters. According to the design requirements of passive EMI filters, the cutoff frequency of passive EMI filters can be increased, thereby reducing the value of the common-mode inductance of passive EMI filters and reducing the overall size of EMI filters. This effectively solves the problem of low power density of power electronic converters after adding EMI filters, while meeting the requirements of conducted frequency band noise attenuation. It also provides design indicators and mathematical models for full-band compact hybrid EMI filters and quantitatively analyzes the effect of hybrid EMI filters.

[0131] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0132] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0133] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A current feedback based full-band compact hybrid EMI filter circuit design method, characterized in that, Includes the following steps: Based on a linear stable impedance network, an electromagnetic interference test circuit was built to obtain the common-mode EMI spectrum required for attenuation of the PWM converter, and a high-frequency equivalent circuit of the PWM converter was established. Based on the high-frequency equivalent circuit of the PWM converter, high-frequency equivalent models of active and passive EMI filter circuits are constructed. According to the high-frequency equivalent models of the active and passive EMI filter circuits and the noise attenuation characteristics of the hybrid EMI filter circuit topology, the optimal hybrid EMI filter topology is obtained, including: dividing the hybrid EMI filter topology into two combinations based on different combinations of the active and passive EMI filter circuits: passive EMI filter close to the interference source and active EMI filter close to the interference source; drawing the equivalent circuit model based on the common-mode noise conduction loop and obtaining the insertion loss expression describing the filtering effect, wherein the insertion losses of the two combinations are respectively: ， in, IL 1 is the insertion loss model of a passive EMI filter when it is close to an interference source. IL 2 is the insertion loss model of an active EMI filter when it is close to an interference source. V L1 This refers to the common-mode voltage across the equivalent impedance of the linearly stable impedance network without an EMI filter. V L2 This refers to the common-mode voltage across the equivalent impedance of the LISN terminal after installing an EMI filter. Z s and Z L These are the equivalent impedances of the common-mode interference source and the equivalent impedance of the LISN terminal, respectively. Z Lcm and Z cy These are the common-mode inductance and grounding capacitance values ​​of the passive EMI filter, respectively. B i Let be the current amplification factor of the equivalent controlled source model of the active EMI filter; subtracting the insertion loss expressions of the different models above yields the expression describing the difference in filtering effect: ； Based on the noise cancellation principle of the active EMI filter and the common-mode EMI spectrum, an active EMI filter topology is designed; based on the common-mode EMI noise spectrum after adding the active EMI filter, a passive EMI filter structure is designed. The hybrid EMI filter circuit is designed based on the hybrid EMI filter topology, the active EMI filter topology, the passive EMI filter structure, and the high-frequency equivalent model of the active and passive EMI filter circuits.

2. The method of claim 1, wherein, The circuit may include an active EMI filter circuit and a passive EMI filter circuit, wherein, The active EMI filter circuit consists of a frequency selection network, a phase compensator, an amplification network, and a passive injection network, and is used to attenuate the noise amplitude within the inherent bandwidth of the active network. The passive EMI filter circuit consists of a common-mode inductor and a grounding capacitor, and is used to attenuate the amplitude of high-frequency noise that is not attenuated by the active EMI filter circuit.

3. The method of claim 2, wherein, In the high-frequency equivalent model of the active EMI filter, the frequency-selective network is composed of capacitors. C s1 and resistance R s1 The first-order high-pass network is constructed, wherein the passive injection network consists of capacitors. C in and resistance R in Composition; Based on the high-frequency equivalent model of the active EMI filter, the insertion loss expression and closed-loop transfer function of the active EMI filter are obtained: in, V L This refers to the common-mode voltage across the equivalent impedance of the linearly stable impedance network without an EMI filter. V ’ L The common-mode voltage across the equivalent impedance of the linear stable impedance network after adding an EMI filter. I L The current flowing into the equivalent impedance of the linear stable impedance network, Z S The equivalent impedance of the common-mode interference source. Z L This represents the equivalent impedance value of a linear stable impedance network. T comp (s) is the transfer function of the system's phase compensator. G b (s) is the closed-loop transfer function of the operational amplifier. s For Laplace variables.

4. The method according to claim 1, characterized in that, Based on the common-mode EMI spectrum when the active EMI filter circuit is installed, the insertion loss of the active EMI filter circuit, and the passive EMI filter structure, the parameters of the passive EMI filter circuit are designed, including: The common-mode inductance of the passive EMI filter circuit without the active EMI filter is calculated using the following formula. L eq1 The common-mode inductor of the passive EMI filter circuit when the active EMI filter is added. L eq2 Inductance ratio: Among them, the point at which the insertion loss curve of the passive EMI filter first becomes tangent to the common-mode EMI noise spectrum to be attenuated before the active EMI filter is installed is... a ( f a , M a The point at which the common-mode EMI noise spectrum, before and after the installation of the active EMI filter, first becomes tangent to the desired attenuation level is... b ( f b , M b ), Δ M It is the difference between the excessive EMI spectrum with and without the active EMI filter. C eq1 and C eq2 These represent the Y-capacitance values ​​of the passive EMI filter without the active EMI filter and the Y-capacitance values ​​of the passive EMI filter with the active EMI filter installed, respectively. The parameters of the passive EMI filter circuit are designed based on the inductance ratio.

5. The method of claim 1, wherein, The hybrid EMI filter circuit is designed based on the hybrid EMI filter topology, the active EMI filter topology and parameters, and the passive EMI filter structure and parameters, wherein the insertion loss expression of the hybrid EMI filter is: in, I L This refers to the common-mode current across the equivalent impedance of the linearly stable impedance network without an EMI filter. I Lt To determine the common-mode current across the equivalent impedance of the linear stable impedance network after adding an EMI filter. G (s) is the closed-loop transfer function of the active EMI filter. Z Cy Here is the impedance value of the Y capacitor in the passive EMI filter. Z Lc This represents the impedance value of the common-mode inductor in the passive EMI filter. Z L The equivalent impedance of a linear stable impedance network. s For Laplace variables.

6. The method of claim 1, wherein, The hybrid EMI filter circuit described herein is applicable to all PWM converters, and the design method described herein is applicable to the suppression of conducted common-mode and differential-mode EMI.

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