A hybrid EMI suppression method and filter based on controllable Y-capacitor

Abstract

The application relates to a controllable Y capacitor-based hybrid EMI suppression method and filter, and the method comprises the following steps: based on the substitution theorem, a control tube and a freewheeling tube of a DC / DC converter are respectively equivalent to a voltage source and a current source, an equivalent CM behavior model is established, and the transmission relationship between a noise source and common-mode noise is determined; a common-collector common-base broadband amplification architecture is used to construct a hybrid EMI filter, an active EMI filter circuit of the hybrid EMI filter is equivalent to a controllable Y capacitor, and an equivalent relationship between the controllable Y capacitor and a physical Y capacitor is established; an LC filter circuit is formed by the controllable Y capacitor and a common-mode choke coil, and is connected to an input bus of the DC / DC converter; according to the equivalent relationship between the controllable Y capacitor and the physical Y capacitor, the equivalent capacitance of the controllable Y capacitor is adjusted, noise attenuation matching is realized, and thus dynamic suppression of common-mode noise is realized. Compared with the prior art, the application has the advantages of improving the full-band dynamic EMI suppression performance of the converter and reducing the size of the filter.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic interference filtering technology, and in particular to a hybrid EMI suppression method and filter based on a controllable Y capacitor. Background Technology

[0002] With the widespread application of third-generation semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) in power converters, their high-frequency switching characteristics, fast rise times, and high voltage and current waveforms have enabled significant progress in improving efficiency and power density. However, these characteristics have also led to increasingly prominent electromagnetic interference (EMI) problems, especially common-mode (CM) noise in conducted EMI. Common-mode noise propagates through power lines and grounding systems, potentially causing performance degradation of internal circuits, signal distortion, and even equipment failure, seriously threatening system reliability and stability.

[0003] In practical applications, traditional EMI suppression methods mainly rely on passive EMI filter circuits (PEFs), which are typically composed of components such as common-mode inductors, Y capacitors, and X capacitors. However, these passive components are relatively large, limiting further miniaturization and integration of power converters. Active EMI filter circuits (AEFs), due to their high integration and good suppression of low-frequency noise, have become an effective means of solving this problem. However, the suppression effect of active filters in the high-frequency range is limited by the gain-bandwidth product of the operational amplifier, and their parasitic parameters in the high-frequency range affect filtering performance. Therefore, hybrid EMI filters (HEFs) have emerged, aiming to combine the advantages of passive and active filters while compensating for their respective shortcomings.

[0004] Hybrid EMI filters based on controllable Y capacitors significantly improve filter performance by introducing active Y capacitors. The active Y capacitor, through a high-pass filter, broadband amplifier, and injection circuit, effectively expands the equivalent Y capacitance value at high frequencies, thereby enhancing high-frequency EMI suppression. Compared to traditional passive Y capacitors, active Y capacitors significantly improve high-frequency filtering while maintaining low-frequency safety. However, hybrid EMI filters based on controllable Y capacitors still face some challenges, such as the impact of high-frequency parasitic effects, the stability of active circuits, and cost.

[0005] A search revealed Chinese invention patent application publication number CN113991987A, which discloses a common-mode current detection and suppression system, comprising: an RC circuit connected in parallel with a switching transistor of the circuit to be detected and suppressed; the RC circuit having an adjustable capacitor; a passive EMI filter including a common-mode choke, an adjustable Y capacitor, and an X capacitor; wherein the common-mode choke is connected to the positive and negative power lines of the circuit to be detected and suppressed, the adjustable Y capacitor is connected between the power supply and ground of the circuit to be detected and suppressed, and the X capacitor is connected between the power lines; an extraction module for acquiring the oscillation waveform of the drain-source voltage of the circuit to be detected and suppressed; an analog-to-digital conversion module for digitizing the oscillation waveform acquired by the extraction module to obtain a discrete digital signal; a digital signal processing module for analyzing and processing the discrete digital signal obtained by the analog-to-digital conversion module to obtain a control adjustment signal; and an adjustment module for adjusting the capacitance values ​​of one or more of the adjustable capacitors in the RC circuit and the adjustable Y capacitors in the passive EMI filter according to the control adjustment signal obtained by the digital signal processing module, thereby realizing common-mode current detection and suppression. The existing patent application has the problem of using a passive EMI filter, which is bulky and difficult to integrate into the power converter.

[0006] Improving the EMI suppression and stability performance of hybrid EMI filters has become a technical problem that needs to be solved. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art by providing a hybrid EMI suppression method and filter based on a controllable Y capacitor.

[0008] The objective of this invention can be achieved through the following technical solutions: According to a first aspect of the present invention, a hybrid EMI suppression method based on a controllable Y capacitor is provided, the method comprising: Based on the substitution theorem, the control transistor and freewheeling transistor of the DC / DC converter are respectively equivalent to voltage sources and current sources. An equivalent CM behavior model is established to determine the transmission relationship between noise sources and common-mode noise. A hybrid EMI filter is constructed using a common-collector, common-base broadband amplification architecture. The active EMI filtering circuit of the hybrid EMI filter is equivalent to a controllable Y capacitor, and an equivalent relationship between the controllable Y capacitor and the physical Y capacitor is established. A controllable Y capacitor and a common-mode choke are combined to form an LC filter circuit, which is then connected to the input bus of the DC / DC converter. Based on the equivalent relationship between the controllable Y capacitor and the physical Y capacitor, noise attenuation matching can be achieved by adjusting the equivalent capacitance value of the controllable Y capacitor, thereby dynamically suppressing common-mode noise.

[0009] As a preferred technical solution, the equivalent relationship between the controllable Y capacitor and the physical Y capacitor satisfies: , Among them, C y Let G1(s) be the physical Y capacitor, G2(s) be the noise detection transfer function, and G2(s) be the noise amplification transfer function. This is the equivalent capacitance of the controllable Y capacitor.

[0010] As a preferred technical solution, in the common-collector common-base broadband amplification architecture, the first-stage common-collector electrode circuit is provided with a compensation capacitor C connected in parallel with the lower bias resistor. b1 The second-stage common-base circuit includes a compensation capacitor C connected in parallel with the base bias resistor. b3 .

[0011] As a preferred technical solution, in the equivalent CM behavior model, one end of the voltage source is connected to the parasitic impedance Z. SG The other end is connected in series with the parasitic inductance impedance Z of the input wire. Lwire Common mode choke impedance Z LD and LISN equivalent common-mode impedance Z CM The equivalent impedance Z of the controllable Y capacitor AEF With Z SG After being connected in parallel, they form branch impedances Z2 and Z. CM Z Lwire Z LD The series connection forms the total impedance Z1.

[0012] As a preferred technical solution, the transmission relationship between the noise source and the common-mode noise is as follows: the common-mode noise is dominated by the voltage source, and its amplitude is directly related to the rate of change of the switching voltage and the parasitic capacitance CSG of the converter half-bridge midpoint to ground.

[0013] As a preferred technical solution, the transmission relationship between the noise source and the common-mode noise satisfies: , Among them, Z SG Parasitic capacitance C SG The equivalent impedance; The common-mode impedance of LISN Parasitic inductance and impedance of the input wires of a DC / DC converter Impedance of common-mode choke LD series impedance, For controllable Y capacitor impedance and Z SG Parallel impedance; As a noise source, This is common-mode noise.

[0014] As a preferred technical solution, in the LC filter circuit, the controllable Y capacitor is connected in parallel between the input bus and the ground, and the two windings of the common-mode choke are connected in series in the positive input bus and the negative input bus, respectively, forming a common-mode noise suppression path.

[0015] According to another aspect of the present invention, a hybrid EMI filter based on a controllable Y capacitor is provided. The hybrid EMI filter circuit is used to implement the method as described in any one of the first aspects. The hybrid EMI filter includes an active EMI filter circuit and a passive EMI filter circuit. The active EMI filter circuit includes a noise detection unit, a common-collector-common-base amplifier circuit, and a noise injection unit connected in sequence. The passive EMI filter circuit is composed of a common-mode choke. The common-collector-common-base amplifier circuit is a broadband amplifier circuit with two cascaded transistors. The first stage is the common-collector input stage, and the second stage is the common-base amplification output stage. Together with a bias network, coupling elements, and a compensation network, it is used to achieve high bandwidth and high stability common-mode noise amplification, and to meet the requirements of high-frequency EMI suppression.

[0016] As a preferred technical solution, the lower bias resistor of the common collector input stage is connected in parallel with a compensation capacitor Cb1, and the base bias resistor of the common base amplification output stage is connected in parallel with a compensation capacitor Cb3.

[0017] As a preferred technical solution, the noise detection unit includes two completely symmetrical and parallel detection branches that jointly collect the common-mode noise voltage of the input bus. The noise injection unit includes a physical Y capacitor and an injection resistor. One end of the noise injection unit is connected to the output of the common-collector-common-base amplifier circuit, and the other end is connected to the input of the DC / DC converter.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1) This invention establishes an equivalent CM behavior model through the substitution theorem, equates the active circuit to a controllable Y capacitor, and constructs an LC filter circuit by combining a common-mode choke. This complete technical solution fundamentally breaks through the safety leakage current limitation of traditional passive Y capacitors, realizes dynamic suppression of common-mode EMI across the entire frequency band through the synergy of active compensation and passive filtering, significantly improves the EMI suppression performance of high-frequency DC / DC converters, and significantly reduces the size of the filter. It has outstanding creativity and engineering practicality.

[0019] 2) By clarifying the equivalent relationship between the controllable Y capacitor and the physical Y capacitor, this invention establishes a quantitative correspondence between the equivalent capacitance value and the circuit gain. It can achieve low-frequency common-mode noise compensation with an equivalent large capacitance value without increasing the physical Y capacitor value or violating safety regulations. This perfectly solves the core contradiction between the "noise reduction requirement and leakage current limitation" of traditional Y capacitors and improves the compliance and practicality of the solution.

[0020] 3) In the common-collector-common-base broadband amplifier architecture, by setting parallel compensation capacitors C in both stages of the circuit... b1 C b3 This effectively expands the high-frequency loop bandwidth of the circuit, optimizes the high-frequency phase margin, suppresses high-frequency self-oscillation, and significantly improves the high-frequency stability of the amplifier circuit, enabling it to adapt to the high-speed switching noise generated by third-generation semiconductor devices and meet the EMI suppression requirements of high-frequency converters.

[0021] 4) This invention clarifies the core conclusion that common-mode noise in the 150kHz-30MHz EMI test band is dominated by voltage sources through decoupling analysis, and reveals the direct correlation between the common-mode noise amplitude and the rate of change of switching voltage and the parasitic capacitance of the half-bridge midpoint to ground. This provides clear theoretical guidance for the targeted design of subsequent filter circuits and greatly improves the accuracy and effectiveness of EMI suppression.

[0022] 5) The hardware connection structure of the LC filter circuit was clarified. The controllable Y capacitor is connected in parallel between the input bus and the ground. The dual windings of the common-mode choke are connected in series with the positive and negative input buses respectively, forming a full-band common-mode suppression path that combines active compensation and passive filtering. This solves the problem of insufficient low-frequency suppression through the active circuit and ensures high-frequency suppression through the passive choke, while also realizing the miniaturization design of the filter. Attached Figure Description

[0023] Figure 1 A schematic diagram of a LISN-based Buck DC / DC converter test platform provided for an embodiment of the present invention; Figure 2 A schematic diagram of a Buck DC / DC converter circuit model based on LISN provided for an embodiment of the present invention; Figure 3 A schematic diagram of an equivalent circuit model of a Buck DC / DC converter provided for an embodiment of the present invention; Figure 4 A schematic diagram of a common-mode equivalent circuit model of a Buck DC / DC converter based on a current source, provided for an embodiment of the present invention; Figure 5 A schematic diagram of a common-mode equivalent circuit model of a Buck DC / DC converter based on a voltage source, provided for an embodiment of the present invention; Figure 6 A schematic diagram of the overall structure of an active EMI filter circuit with a controllable Y capacitor provided in an embodiment of the present invention; Figure 7 A schematic diagram of the equivalent circuit model of an active EMI filter circuit with a controllable Y capacitor provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the equivalent circuit model of common-mode EMI provided in an embodiment of the present invention; Figure 9 This is a schematic flowchart of a hybrid EMI suppression method based on a controllable Y capacitor in this invention. Figure 10 This is a comparison of the spectrum before and after hybrid EMI suppression based on a controllable Y capacitor. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0025] Example 1 This embodiment relates to a hybrid EMI filter based on a controllable Y capacitor, such as... Figure 6 A hybrid EMI filter comprises active and passive components, namely active EMI filtering circuits and passive EMI filtering circuits. The active component consists of a noise detection unit (C...). sen R sen ), noise amplification unit (common-collector common-base amplifier circuit, in which resistor R is added) b1 and capacitor C b1 To improve the high-frequency characteristics of the circuit) and noise injection unit (C y R inj The three parts are connected in sequence, and the passive part consists of a common-mode choke L. D Composition. At low frequencies, common-mode chokes have good suppression effects. At high frequencies, due to the influence of parasitic parameters, the suppression effect of common-mode chokes deteriorates, while common-collector-common-base amplifier circuits have good high-frequency characteristics and can compensate for this deficiency.

[0026] The noise detection unit includes two completely symmetrical and parallel detection branches that jointly acquire the common-mode noise voltage of the input bus. v cm The two detection branches are a positive bus noise detection branch and a negative bus noise detection branch. The positive bus noise detection branch includes a detection capacitor C connected in series. sen1and detection resistor R sen1 C sen1 One end is connected to the positive bus of the LISN output, and the other end is connected to R. sen1 One end; R sen1 The other end is connected to the input node of the noise amplification unit and also connected to the bias network. The negative bus noise detection branch includes a detection capacitor C connected in series. sen2 and detection resistor R sen2 C sen2 One end is connected to the negative bus of the LISN output, and the other end is connected to R. sen2 One end; R sen2 The other end is connected to the input node of the noise amplification unit, and R sen1 Connecting.

[0027] Detection capacitor C sen and detection resistor R sen C sen One end is connected to the LISN output to acquire the common-mode voltage. v cm C sen The other end is connected to R sen It is then connected to the input terminal of the amplification unit.

[0028] The noise amplification unit includes a bias resistor R b1 R b2 Compensation capacitor C b1 And amplifying transistors; R b1 With C b1 It is connected in series and then in parallel in the base circuit of the amplifier tube to improve high-frequency characteristics.

[0029] The noise injection unit includes a physical Y capacitor C y and injection resistance R inj The output of the noise amplifier unit is connected to C. y With R inj A series branch, the other end of which is connected to the converter input, forms a noise compensation current injection path. Physical Y capacitor C y It adopts a dual-path symmetrical structure, consisting of C y1 C y2 It consists of two capacitors, which correspond to the positive and negative input bus noise compensation injection branches respectively, and are connected in series with the injection resistor to form a dual-path symmetrical noise injection circuit.

[0030] Example 2 This embodiment relates to a hybrid EMI suppression method based on controllable Y capacitors, which aims to optimize the circuit design of active Y capacitors, reduce the influence of parasitic parameters, improve the dynamic response speed of filters, and reduce costs, so as to promote the widespread application of hybrid EMI filters based on controllable Y capacitors in power converters with high power density and high electromagnetic compatibility, provide a more efficient and compact solution for EMI suppression of power converters, and promote the development of electromagnetic compatibility technology.

[0031] The principle of this method is as follows: First, the generation and conduction mechanism of common-mode EMI in the converter is analyzed, and the high-frequency parasitic parameters contained in the converter circuit model are determined to obtain the common-mode EMI model of the power converter system. Second, an equivalent controllable Y-capacitor model based on the substitution theorem is established using an active filter circuit, and an LC filter circuit is formed with a common-mode choke to suppress CM noise. In this process, the use of large capacitors and large inductors is avoided.

[0032] For Buck DC / DC converters, the EMI suppression process is as follows: Figure 9 ,include Step one: Analyze the EMI conduction path of the Buck DC / DC converter to determine the main high-frequency parasitic parameters in the power converter. Besides the basic circuit components, its main high-frequency parasitic parameters are determined by the high-frequency parasitic inductance L of the input conductors. wire (Including the parasitic inductance L of the parallel input wires) wire1 and L wire2 And the converter's parasitic capacitance to ground C SG The parasitic parameters mentioned above have a major impact on CM noise, and these parameters can be measured using an impedance network analyzer.

[0033] Step two, according to Figure 1 Build a LISN-based DC / DC converter test platform. For example, a Buck DC / DC converter test model, such as... Figure 2 Including DC source V DC LISN (Linear Impedance Stabilized Network), Buck DC / DC converter, parasitic capacitance from the midpoint of the converter half-bridge to ground (referred to as parasitic capacitance) C SG The output load R and ground. The LISN includes an isolation circuit composed of inductors L1 and L2, and C. N R N R L C L The high-frequency noise measurement branch is composed of the Buck DC / DC converter, which includes the output filter inductor L. out Output capacitor C out And output resistance R, input wire parasitic inductance L wire1 and L wire2Input capacitor C in Control tube Q1, freewheeling tube Q2, where C SG This is the lumped parasitic capacitance to ground at the midpoint of the half-bridge of the Buck DC / DC converter.

[0034] The drain of control transistor Q1 is connected to the positive input of the converter, and the source of control transistor Q1 is connected to the drain of freewheeling transistor Q2, forming the midpoint of the half-bridge; the source of freewheeling transistor Q2 is connected to the negative input of the converter and grounded; the midpoint of the half-bridge is connected to the output filter inductor L. out Connect the output capacitor C out The positive terminal of the output capacitor Cout is connected to one end of the load resistor R; the negative terminal of the output capacitor Cout is grounded together with the other end of the load resistor R; the input capacitor C in Parallel connection between the positive and negative input terminals of the converter; parasitic inductance L of the input wire wire1 The parasitic inductance L of the input wire is connected in series in the positive input line of the converter. wire2 It is connected in series in the negative input circuit of the converter; the midpoint of the half-bridge is connected through the parasitic capacitance C. SG Connected to the earth.

[0035] Based on the LISN test platform, the CM noise of the Buck DC / DC converter is caused by the high dv / dt of the control transistor Q1 during switching, which is transmitted through the parasitic capacitance C. SG Caused by the instantaneous voltage change during switching, passing through C. SG Forming common-mode current I CM The path is: Converter → C SG →Earth→LISN→Converter, forming a closed loop, such as Figure 1 As shown.

[0036] Step 3: Based on the substitution theorem, establish an equivalent CM behavior model for the EMI conduction path in the Buck DC / DC converter based on LISN.

[0037] A converter CM behavior model is established based on the substitution theorem, such as... Figure 2 and Figure 3 As shown, Figure 2 This is the circuit model of the Buck DC / DC converter. Figure 3 We then construct its equivalent CM behavior model. Switches Q1 and Q2 are respectively represented as voltage sources V. ds With current source I d This simplifies the noise sources and coupling paths of the CM. Voltage source V ds One end is connected to the parasitic impedance Z SG The other end is connected in series with Z Lwire Z LD and LISN equivalent common-mode impedance Z CM The equivalent impedance Z of the controllable Y capacitor AEF With ZSG After being connected in parallel, they form branch impedances Z2 and Z. CM Z Lwire Z LD The series connection forms the total impedance Z1.

[0038] The high dv / dt generated during the Q1 switching process is coupled through components such as parasitic capacitance, forming a noise source; V ds and I d Interacting with parasitic parameters, CM noise sources and conduction paths are formed. The equivalent circuit model provides a clear framework for subsequent EMI analysis and noise suppression.

[0039] Step four involves analyzing the impact of current sources and voltage sources on the CM noise of the power converter, determining the relationship between CM noise and noise sources, constructing equivalent models for the current source and common-mode noise of the voltage source, and confirming that the noise in the 150kHz–30MHz frequency band is dominated by the voltage source. Figure 4 and Figure 5 .

[0040] The voltage source V is analyzed below. ds With current source I d Common-mode (CM) noise propagation path: Current source equivalent model: when only the current source I is considered d At times, such as Figure 4 As shown, the voltage source V ds After a short circuit, retain current source I. d Current source I d One end is connected to the parasitic capacitance C SG One end, C SG The other end is connected to ground; the ground is connected to the return current source I via LISN, the parasitic inductance of the input wire, and so on. d At the other end, a closed noise loop is formed: I d →C SG →Earth→LISN→Input Wire→I d In this path, CM noise is caused by I d It is coupled to the grounding loop via parasitic capacitance.

[0041] Common-mode equivalent model of voltage source: when only the voltage source V is considered ds At times, such as Figure 5 As shown, current source I d After opening the circuit, retain the voltage source V. ds Voltage source V ds One end is connected to the parasitic capacitance C SG C SG The other end is connected to ground; ground is connected back to the voltage source V via LISN and the parasitic inductance of the input wire. dsAt the other end, a common-mode noise path is formed. V ds The high dv / dt (rate of change of switching voltage) is achieved through C SG The path to generate CM noise is: V ds →C SG →Earth→LISN→Input Wire→V ds At this time, the output L out C out R is negligible due to its high impedance. In the frequency range of 150kHz-30MHz, the input capacitance C... in It exhibits low impedance (approximately short circuit), resulting in I d C in Bypassing significantly reduces its contribution to CM noise. Therefore, CM noise in this frequency band is mainly caused by V ds Dominant, its amplitude is related to dv / dt and C SG The value is directly related. This analysis indicates that high-frequency EMI suppression should focus on V. ds The path was optimized.

[0042] To simplify this common-mode circuit model, the simplified CM impedance of the LISN is: , in, This is the CM impedance of the LISN, i.e., the common-mode equivalent impedance; For capacitor C L impedance; For resistor R L impedance; For capacitor C N impedance; For resistor R N The impedance.

[0043] C in Considered a short circuit, the CM impedance of the Buck DC / DC converter is... , Among them, Z Lwire1 For L wire1 The impedance, Z Lwire2 For L wire2 The impedance, Z CSG C SG The impedance.

[0044] Step 5: Construct the active EMI filter circuit and determine its circuit architecture, such as... Figure 6 As shown.

[0045] The noise amplification unit adopts a two-stage cascaded common-collector-common-base (CC-CB) broadband amplifier circuit. The first stage is the common-collector input stage, and the second stage is the common-base amplification output stage. Together with the bias network, coupling element, and compensation network, it achieves high bandwidth and high stability common-mode noise amplification, which is suitable for high-frequency EMI suppression requirements.

[0046] The first-level bias network includes: Upper bias resistor R b2 One end is connected to +12V, and the other end is connected to the base of Q1 to provide a positive bias to the base; Lower bias resistor R b1 One end is connected to the base of Q1, and the other end is grounded, and connected to R. b2 The voltage divider determines the static operating point of Q1; Emitter resistor R e1 Connected in series between the emitter of Q1 and ground, it stabilizes the static operating point and improves circuit stability; Compensation capacitor C b1 Parallel connection in R b1 Both ends are used to extend high-frequency bandwidth, compensate for high-frequency phase, and suppress self-excited oscillation.

[0047] The second-stage bias network includes: Base bias resistor R b3 R b4 :R b4 One end is connected to +12V, and the other end is connected to the base of Q2; R b3 One end is connected to the base of Q2, and the other end is grounded. The voltage divider provides a fixed DC bias to the base of Q2. Emitter resistor R e2 Connected in series between the emitter of Q2 and ground, it stabilizes the static operating point; collector resistor R c1 R c2 :R c1 Connected in series between the collector of Q2 and +12V, R c2 Connected in series between the collector of Q2 and ground, it forms a collector load, amplifying the current and converting it into a voltage output; Compensation capacitor C b3 Parallel connection in R b3 Both ends are used for high-frequency phase compensation, improving the stability of the high-frequency loop and suppressing self-oscillation.

[0048] Step 6: Based on the active EMI filter circuit, the substitution theorem is used to convert the active EMI filter circuit into a controllable Y capacitor model, and the relationship between the physical Y capacitor and the controllable Y capacitor is analyzed.

[0049] The active filter circuit is equivalent to a small-signal model and simplified, such as... Figure 6 and Figure 7 As shown, Figure 6 For the equivalent circuit model, Figure 7 To simplify its circuit model. Figure 6 In this context, the entire active filter circuit is equivalent to a controllable Y capacitor C. AEF C AEF One end is connected to the LISN output, and the other end is connected to ground; the controllable Y capacitor C AEF With common mode choke L D Construct an LC filter circuit, L D It is connected in series in the positive and negative input circuits.

[0050] The relationship between the transfer function and the circuit parameters is as follows: , , in, , , , , , , , , , in, Here is the noise detection transfer function. For input common-mode noise voltage, Output voltage for noise detection. The equivalent input impedance of the noise detection branch. For noise detection capacitor C sen The equivalent impedance; The noise amplification transfer function is... This refers to the output voltage of the common-collector-common-base amplifier circuit. For transistor transconductance, This is the base-emitter equivalent impedance of the transistor. Interstage / output coupling capacitors C u2 The equivalent impedance, Input coupling capacitor C u2 The equivalent impedance, The total impedance of the collector load is... This represents the total impedance of the common-collector base-biased network. noise detection resistor R sen impedance, The total impedance is the emitter resistance. The input impedance of the common collector (emitter follower) stage. The input impedance of the common-base stage. The total impedance of the noise detection branch; The equivalent impedance of the bias branch under the common collector stage. The impedance of the bias resistor Rb2 on the common collector stage. The impedance of the emitter resistor Re1 of the common collector Q1 is... For the common collector Q2 emitter resistor R e2 impedance, The common-base collector pull-up resistor R of the displacement common-base stage Q2 c1 impedance, The common-base collector pull-down resistor R is... c2 impedance, The series equivalent impedance of the bias branch under the common collector stage. The bias resistor R of the common collector stage b1 impedance, To compensate capacitor C b1 The equivalent impedance, The base-emitter resistance r of the transistor be The impedance (corresponding to the r of the first-stage common-collector transistor Q1) be1 And the r of the second-stage common-base transistor Q2 be2 ), The base-emitter junction capacitance C of the transistor be The equivalent impedance, The equivalent impedance of the positive busbar noise detection branch is... The equivalent impedance of the negative bus noise detection branch.

[0051] Step 7: The capacitance value of the controllable Y capacitor is obtained by adjusting the parameters of the active EMI filter circuit, and it is combined with the common mode choke to form an LC filter circuit to filter the circuit. Then, LISN is used to measure the CM noise waveform before and after the mixed EMI suppression based on the controllable Y capacitor to determine the EMI level after suppression.

[0052] Determine the inductance of the common-mode choke: By comparing the CM noise measured by LISN or simulation with the EMI standard limit, determine the EMI noise amplitude that needs to be attenuated. Select the highest point of the low-frequency spectrum to be suppressed as the reference point, and design using a second-order filter. The formula is as follows: , , , in, For corner frequency, The highest frequency in the low spectrum. M c In order to be in f c The target attenuation is given by L, where L is the inductance of the common-mode choke. This is the equivalent capacitance of the controllable Y capacitor. Let π be the mathematical constant, and s denote the Laplace field. Here is the noise detection transfer function. The noise amplification transfer function is... This is the capacitance value of the physical Y capacitor.

[0053] Based on the above theory, the EMI suppression process of DC / DC converters can be summarized as the following steps: 1) such as Figure 3 , voltage source V ds Replacement control transistor Q1, current source I d Replacing the freewheeling diode Q2 is a method for simplifying and equivalently modeling the power converter circuit. Here, the voltage source represents the switching control of Q1, and its behavior produces a similar voltage change to control the current; the current source I... d The freewheeling function of Q2 is simulated to ensure smooth current flow. The switching action of control transistor Q1 affects the circuit voltage; replacing it with a voltage source directly reflects its driving characteristics. Freewheeling transistor Q2 provides a continuous path for the current, and current source I... d The substitute can accurately simulate changes in current.

[0054] 2) Based on circuit analysis, the effects of current and voltage sources are considered separately, and a decoupling model is established. Building upon this model, and considering the influencing factors of both current and voltage sources, the entire circuit model is optimized. Taking into account parasitic effects, current-voltage interactions, and filtering suppression measures, a more accurate equivalent common-mode (CM) electromagnetic interference (EMI) model for the Buck DC / DC converter is derived. This model clearly establishes the relationship between CM noise sources and CM noise, providing theoretical support for noise source localization, isolation, and suppression, and guiding electromagnetic compatibility design optimization.

[0055] 3) The active EMI filter circuit is modeled as a controllable Y-capacitor, and its mathematical relationship with the physical Y-capacitor is established. In this process, by analyzing the voltage feedback mechanism and current compensation characteristics in the active circuit, the mathematical expression for the controllable Y-capacitor can be derived. Precise control of the controllable Y-capacitor is achieved through parameter optimization, and an LC filter circuit is constructed for noise suppression verification. Specifically, by adjusting key parameters such as amplifier gain and feedback network impedance, the equivalent Y-capacitor value can be adjusted as needed across a wide frequency range. The optimized controllable Y-capacitor and a common-mode choke form an adjustable LC filter. Its resonant frequency can be precisely matched to the noise frequency band through dynamic adjustment of the capacitor value, thereby achieving EMI attenuation and providing strong support for electromagnetic compatibility (EMC) optimization.

[0056] Example 3 This embodiment also relates to a hybrid EMI suppression method based on a controllable Y capacitor. Targeting high-voltage, high-frequency, high-power DC / DC converter systems, the active component of the hybrid EMI filter is first studied, and a CM behavior model of the controllable Y capacitor is established. Then, the relationship between the Y capacitor and the controllable Y capacitor is determined, and a hybrid EMI filter based on the controllable Y capacitor is established. By adjusting the controllable LC filter circuit, noise suppression by the hybrid EMI filter is achieved. This method has significant engineering value for the development of high-power, high-frequency DC / DC applications and the optimization of the EMC characteristics and EMI suppression of converter systems.

[0057] The method includes: like Figure 1 A linear stable impedance network (LISN) is connected between the DC / DC converter and the input power supply, such as... Figure 6 and Figure 7 Connect the hybrid EMI filter between the linear stable impedance network and the converter. Connect the output of the hybrid EMI filter to the voltage input of the Buck DC / DC converter. Connect the ground terminal of the Buck DC / DC converter to the output of the LISN. Connect the input of the LISN to the negative output of the DC input power supply VDC and connect them to the ground. Connect the output of the Buck DC / DC converter to the load resistor R. Connect the other end of the load resistor R to the system ground.

[0058] Use common mode voltage v cm The CM noise experienced by the LISN is represented by G1(s) and G2(s), which represent the transfer functions of the noise injection and noise amplification circuits, respectively. The flow through capacitor C is determined. y current i inj With common-mode voltage v cm The relationship is: , , , In the formula, To compensate for the injected circuit, For physical Y capacitors, The impedance of the physical Y capacitor. v cm C is the common-mode voltage detected by LISN. AEF This is the equivalent capacitance of the controllable Y capacitor. The equivalent impedance of the controllable Y capacitor.

[0059] Use C AEF Replace [1-G1(s)G2(s)] and C y To represent the controllable Y capacitor connected in parallel with LISN, and using Z AEF This represents the equivalent impedance of the controllable Y capacitor. Therefore, by changing the transfer functions G1(s) and G2(s) to alter the value of the controllable Y capacitor, it is possible to avoid selecting a large value while still meeting the leakage current requirements of the controllable Y capacitor. Controllable Y capacitor C AEF (correspond Figure 8 Z AEF One end of the controllable Y capacitor is connected to the LISN output terminal, and the other end is connected to ground; AEF With common mode choke L D Construct an LC filter circuit, L D It is connected in series in the positive and negative input circuits. Figure 8 In the diagram, S is the midpoint of the converter half-bridge, and G is the protective ground.

[0060] Using the internal noise source of the Buck converter v ds Replacement of switching transistors in DC / DC converters, noise sources v ds Determine the CM noise for the voltage changes generated during the switching process of the replaced device. With noise source v ds The relationship between them is: , , , Among them, Z CM Z represents the CM (common-mode) impedance of the LISN. Lwire =Z Lwire1 ||Z Lwire2 Z represents the equivalent impedance of the DC / DC converter. Lwire1 Z represents the impedance of the voltage input wire of the DC / DC converter.Lwire2 Z represents the impedance of the grounding conductor of the DC / DC converter. LD For common mode choke L D The impedance, Z SG C is the parasitic capacitance to ground of the DC / DC converter switching transistor. SG The equivalent impedance; for , , series impedance, for and Z SG Parallel impedance.

[0061] By equating the noise detection, noise amplification, and noise injection circuits to a controllable Y capacitor, and combining them with a common-mode choke L... D To construct an LC filter circuit, change the equivalent capacitance C of the controllable Y capacitor. AEF This ensures that the resonant point of the LC filter circuit falls within the target noise frequency band, achieving common-mode noise attenuation and thus hybrid EMI suppression. The common-mode noise waveforms before and after suppression are collected using LISN to complete the EMI level verification.

[0062] Example 4 This embodiment also involves the verification of a hybrid EMI suppression method based on a controllable Y capacitor. To verify the effectiveness of the method, the simulation circuit diagram required for the experiment was built in the PSpice for TI simulation software. The simulation experimental parameters include the Buck circuit parameters and the hybrid EMI filter circuit parameters, as shown in Table 1 and Table 2, respectively.

[0063] Table 1

[0064] Table 2

[0065] Figure 10 A comparison of the CM noise spectrum before and after hybrid EMI suppression based on a controllable Y capacitor is presented. It can be seen that after suppression, the hybrid EMI filter circuit exhibits good noise suppression performance across the entire frequency band. At low frequencies, it can achieve 25dB of EMI attenuation, while at high frequencies, it can achieve a maximum of 80dB of EMI attenuation, and even 75dB attenuation at 30MHz. Therefore, the hybrid EMI suppression method based on a controllable Y capacitor proposed in this invention is highly effective.

[0066] Example 4 The electronic device of this invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in read-only memory (ROM) or loaded from a storage unit into random access memory (RAM). The RAM may also store various programs and data required for device operation. The CPU, ROM, and RAM are interconnected via a bus. Input / output (I / O) interfaces are also connected to the bus.

[0067] Multiple components in the device are connected to the I / O interface, including: input units such as keyboards and mice; output units such as various types of displays and speakers; storage units such as disks and optical discs; and communication units such as network interface cards (NICs), modems, and wireless transceivers. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks.

[0068] The processing unit performs the various methods and processes described above. For example, in some embodiments, the methods may be implemented as computer software programs tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program may be loaded and / or installed on the device via ROM and / or a communication unit. When the computer program is loaded into RAM and executed by the CPU, one or more steps of the methods described above may be performed. Alternatively, in other embodiments, the CPU may be configured to execute the methods by any other suitable means (e.g., by means of firmware).

[0069] The functions described above in this document can be performed, at least in part, by one or more hardware logic components. For example, exemplary types of hardware logic components that can be used, without limitation, include: Field Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application Standard Products (ASSPs), System-on-Chip (SoCs), Complex Programmable Logic Devices (CPLDs), and so on.

[0070] The program code used to implement the methods of the present invention can be written in any combination of one or more programming languages. This program code can be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code can be executed entirely on the machine, partially on the machine, as a standalone software package partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0071] In the context of this invention, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media can include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory, optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0072] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A hybrid EMI suppression method based on controllable Y capacitors, characterized in that, The method includes: Based on the substitution theorem, the control transistor and freewheeling transistor of the DC / DC converter are respectively equivalent to voltage sources and current sources. An equivalent CM behavior model is established to determine the transmission relationship between noise sources and common-mode noise. A hybrid EMI filter is constructed using a common-collector, common-base broadband amplification architecture. The active EMI filtering circuit of the hybrid EMI filter is equivalent to a controllable Y capacitor, and an equivalent relationship between the controllable Y capacitor and the physical Y capacitor is established. A controllable Y capacitor and a common-mode choke are combined to form an LC filter circuit, which is then connected to the input bus of the DC / DC converter. Based on the equivalent relationship between the controllable Y capacitor and the physical Y capacitor, noise attenuation matching can be achieved by adjusting the equivalent capacitance value of the controllable Y capacitor, thereby dynamically suppressing common-mode noise.

2. The hybrid EMI suppression method based on a controllable Y capacitor according to claim 1, characterized in that, The equivalent relationship between the controllable Y capacitor and the physical Y capacitor satisfies: ， Among them, C y Let G1(s) be the physical Y capacitor, G2(s) be the noise detection transfer function, and G2(s) be the noise amplification transfer function. This is the equivalent capacitance of the controllable Y capacitor.

3. The hybrid EMI suppression method based on a controllable Y capacitor according to claim 1, characterized in that, In the common-collector common-base broadband amplifier architecture, the first-stage common-collector electrode circuit is equipped with a compensation capacitor C connected in parallel with the lower bias resistor. b1 The second-stage common-base circuit includes a compensation capacitor C connected in parallel with the base bias resistor. b3 .

4. The hybrid EMI suppression method based on a controllable Y capacitor according to claim 1, characterized in that, In the equivalent CM behavior model, one end of the voltage source is connected to the parasitic impedance Z. SG The other end is connected in series with the parasitic inductance impedance Z of the input wire. Lwire Common mode choke impedance Z LD and LISN equivalent common-mode impedance Z CM The equivalent impedance Z of the controllable Y capacitor AEF With Z SG After being connected in parallel, they form branch impedances Z2 and Z. CM Z Lwire Z LD The series connection forms the total impedance Z1.

5. The hybrid EMI suppression method based on a controllable Y capacitor according to claim 1, characterized in that, The transmission relationship between the noise source and common-mode noise is as follows: the common-mode noise is dominated by the voltage source, and its amplitude is directly related to the rate of change of the switching voltage and the parasitic capacitance CSG of the converter half-bridge midpoint to ground.

6. A hybrid EMI suppression method based on a controllable Y capacitor according to claim 1 or 5, characterized in that, The transmission relationship between the noise source and the common-mode noise satisfies: ， Among them, Z SG parasitic capacitance C SG The equivalent impedance; The common-mode impedance of LISN Parasitic inductance and impedance of the input wires of a DC / DC converter Impedance of common-mode choke LD Series impedance, For controllable Y capacitor impedance and Z SG Parallel impedance; As a noise source, This is common-mode noise.

7. The hybrid EMI suppression method based on a controllable Y capacitor according to claim 1, characterized in that, In the LC filter circuit, the controllable Y capacitor is connected in parallel between the input bus and the ground, and the two windings of the common-mode choke are connected in series in the positive input bus and the negative input bus, respectively, forming a common-mode noise suppression path.

8. A hybrid EMI filter based on a controllable Y capacitor, characterized in that, The hybrid EMI filter circuit is used to implement the method as described in any one of claims 1 to 7. The hybrid EMI filter includes an active EMI filter circuit and a passive EMI filter circuit. The active EMI filter circuit includes a noise detection unit, a common-collector-common-base amplifier circuit, and a noise injection unit connected in sequence. The passive EMI filter circuit is composed of a common-mode choke. The common-collector-common-base amplifier circuit is a broadband amplifier circuit with two cascaded transistors. The first stage is the common-collector input stage, and the second stage is the common-base amplification output stage. Together with a bias network, coupling elements, and a compensation network, it is used to achieve high bandwidth and high stability common-mode noise amplification, and to meet the requirements of high-frequency EMI suppression.

9. A hybrid EMI filter based on a controllable Y capacitor according to claim 8, characterized in that, The common collector input stage has a lower bias resistor connected in parallel with a compensation capacitor Cb1, and the common base amplification output stage has a base bias resistor connected in parallel with a compensation capacitor Cb3.

10. A hybrid EMI filter based on a controllable Y capacitor according to claim 8, characterized in that, The noise detection unit includes two completely symmetrical and parallel detection branches that jointly collect the common-mode noise voltage of the input bus. The noise injection unit includes a physical Y capacitor and an injection resistor. One end of the noise injection unit is connected to the output of the common-collector-common-base amplifier circuit, and the other end is connected to the input of the DC / DC converter.

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