EMI filtering method based on dual-frequency spread spectrum and dual-frequency recombination common-mode noise cancellation waveform

Abstract

The invention belongs to the technical field of EMI (Electro-Magnetic Interference) suppression, and relates to an EMI filtering method based on dual-frequency spread spectrum and dual-frequency recombination common-mode noise cancellation waveform, which comprises the following steps of: selecting a frequency as a composition frequency; enabling the EUT to work normally by taking a selected frequency as a switching PWM frequency, and obtaining common-mode noise amplitude data of multiple times of the frequency; acquiring a common-mode voltage amplitude, and calculating an amplitude transformation ratio and an amplitude of an injected offset waveform; acquiring a common-mode voltage amplitude, and calculating the phase of the injected offset waveform; injection offset waveform data is obtained through calculation, and the common-mode voltage is offset; according to the invention, common-mode noise is taken as a main scene, and common-mode suppression can be realized while the size is reduced.

Description

Technical Field

[0001] This invention belongs to the field of EMI suppression technology, specifically relating to an EMI filtering method based on dual-frequency spread spectrum and dual-frequency recombined common-mode noise cancellation waveforms. Background Technology

[0002] Electromagnetic interference (EMI) generated during the operation of power electronic devices can pose a serious threat to surrounding electronic systems if not effectively controlled. With the maturity and widespread adoption of wide-bandgap semiconductor devices, increasing the switching frequency of switching power supplies can improve power density, but this also results in larger instantaneous di / dt and dv / dt. These charge and discharge parasitic capacitances and inductances in the circuit, generating displacement currents and varying magnetic flux. Power electronic converters, due to their operating principle, rely on high-frequency switching to achieve voltage conversion. The high-frequency switching process generates significant switching noise, including conducted and radiated interference, which becomes a crucial factor affecting circuit performance. Conducted interference, propagating through power lines and ground lines, can cause signal distortion within the system; radiated interference, through electromagnetic waves propagating through space, threatens the normal operation of other equipment, especially in sensitive electronic devices.

[0003] However, traditional passive EMI filters suffer from large size, and traditional active EMI filters require additional active components and power supply circuits. With the increasing development of digital controllers, incorporating digital controllers into active filters allows for their multiplexing, reducing filter size. The core principle of existing digital filtering technology is consistent with analog active filtering: noise suppression is achieved through detection feedback and utilizing large feedback gain. This requires the introduction of ADCs and DACs, resulting in higher costs, while the performance remains comparable to analog active filtering.

[0004] Therefore, there is a need for an EMI suppression device or method that can reduce costs and size to solve the above-mentioned technical problems. Summary of the Invention

[0005] This invention aims to provide a digital active EMI filtering method based on dual-frequency spread spectrum and dual-frequency recombined common-mode noise cancellation waveform. This method is suitable for scenarios dominated by common-mode noise and can suppress common-mode interference while reducing the size of the filter.

[0006] This invention provides the following technical solution: an EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveforms, comprising the following steps: Step S1: Select frequency 1 and frequency 2 as the constituent frequencies of the dual-frequency spread spectrum PWM.

[0007] Step S2: Use frequency 1 as the switching PWM frequency to enable the EUT to work normally and obtain common-mode noise amplitude data at multiples of frequency 1; use frequency 2 as the switching PWM frequency to enable the EUT to work normally and obtain common-mode noise amplitude data at multiples of frequency 2.

[0008] Step S3: Turn off the EUT's switching PWM signal, and output a sine wave with an amplitude of 1, arbitrary phase, and a frequency that is a multiple of the first and second frequencies through the DAC. The sine wave data is injected into the positive and negative buses through the injection capacitors to obtain the common-mode voltage amplitude at the current output frequency of the DAC. Calculate the amplitude transformation ratio from the injection point to the common-mode noise observation point at the current output frequency of the DAC, as well as the amplitude of the injected cancellation waveform at the frequency.

[0009] Step S4: Use frequency 1 and frequency 2 as the switching PWM frequencies to enable the EUT to work normally. Output a sine wave with known amplitude, known phase, and frequency that is a multiple of the current PWM frequency through the DAC. Inject the sine wave data into the positive and negative buses through the injection capacitors to obtain the common-mode voltage amplitude at the current output frequency of the DAC and calculate the phase of the injected cancellation waveform at the current output frequency of the DAC.

[0010] Step S5: Calculate the injection cancellation waveform data, output the cancellation waveform data synchronously with the dual-frequency spread spectrum PWM through the DAC, and inject the cancellation waveform data into the positive bus and negative bus through the injection capacitor to cancel the common mode voltage.

[0011] Preferably, step S5 is followed by step S6, which is: measuring the common-mode noise on the LISN, and iteratively adjusting the number of sub-cycles occupied by the first frequency and the number of sub-cycles occupied by the second frequency in the dual-frequency spread spectrum PWM within the allowable range of EUT operating conditions, until the sub-cycle number parameter that minimizes the common-mode noise is found.

[0012] More preferably, step S6 includes the following sub-steps: S61. Within the allowable range of EUT operating conditions, select a set of sub-cycles occupied by frequency 1 and sub-cycles occupied by frequency 2. S62. Measure and record the common-mode voltage on the LISN; S63. Within the allowable range of EUT operating conditions, change the number of sub-cycles occupied by frequency one or frequency two. S64. Repeat S62 and S63 to find the number of sub-cycles occupied by frequency 1 and frequency 2 corresponding to the minimum common-mode noise within the allowable range of EUT operating conditions.

[0013] Preferably, step S1 includes the following sub-steps: S11. Select frequency one and frequency two, and construct the first formula as the mathematical expression for dual-frequency spread spectrum PWM.

[0014] S12. Using the first formula, write a program in the digital controller to produce the final output dual-frequency spread spectrum PWM switching signal.

[0015] The first formula is: (1) In equation (1), P ( t () represents the expression for the dual-frequency spread spectrum modulation PWM signal within one cycle. f c1 Frequency number one. M 1 represents the number of sub-cycles at frequency number one. f c2 It is frequency number two. M 2 represents the number of sub-cycles at frequency 2. D Here, n represents the duty cycle, t represents the sub-cycle number, and t represents time.

[0016] More preferably, step S2 includes the following sub-steps: S21. Program the digital controller to generate a PWM waveform with frequency number one.

[0017] S22. Apply a PWM waveform with frequency 1 to the EUT to make the EUT work normally.

[0018] In S23, the EMI receiver connected via LISN acquires common-mode noise amplitude data at multiples of the first frequency.

[0019] In S24, the digital controller is programmed to generate a PWM waveform with a frequency of frequency two.

[0020] In S25, the EUT is connected to a PWM waveform with frequency number two to enable the EUT to work normally.

[0021] In S26, the EMI receiver connected via LISN acquires common-mode noise amplitude data at multiples of the second frequency.

[0022] More preferably, step S3 includes the following sub-steps: S31. Turn off the EUT's switching PWM signal, and output a sine wave with an amplitude of 1, arbitrary phase, and frequency that is a multiple of the first and second frequencies through the DAC. Inject the sine wave data into the positive and negative buses through the injection capacitors.

[0023] S32. Obtain the common-mode voltage amplitude at the DAC output frequency. Construct a second formula based on the relationship between the injected sine wave amplitude and the common-mode voltage amplitude. Calculate the amplitude ratio from the injection point to the common-mode noise observation point at the frequency based on the second formula.

[0024] S33. Based on the amplitude transformation ratio calculated in step S32 and the common-mode voltage amplitude obtained in steps S23 and S26, construct the third formula, and calculate the amplitude of the multiple injection cancellation waveform at the first and second frequencies according to the third formula.

[0025] The second formula is: (2) In equation (2), G ( kf c )for kf c The amplitude variation from the injection source to the detection point at the frequency point Y mea ( kf c The common-mode voltage amplitude is obtained on the EMI receiver via LISN after injecting a sine wave. The third formula is: (3) In equation (3), Y inj ( kf c )for kf c The common-mode cancellation waveform amplitude required at the frequency point, A ( kf c When the EUT is working properly kf c The common-mode noise amplitude measured at the specified frequency.

[0026] More preferably, step S4 includes the following sub-steps: S41. Using frequency 1 as the switching PWM frequency, the EUT is made to work normally, and the amplitude is sequentially output through the DAC to the value calculated in step S33. Y inj ( kf c1 A sine wave with arbitrarily given phase and frequency that is a multiple of the first frequency is generated. The sine wave data is injected into the positive and negative buses through injection capacitors, and the common-mode voltage amplitude at the corresponding frequencies is recorded sequentially. S42. Using frequency 2 as the switching PWM frequency to ensure normal operation of the EUT, the DAC sequentially outputs amplitudes calculated in S33. Y inj ( kfc2 A sine wave with arbitrarily given phase and frequency that is a multiple of the second frequency is generated. The sine wave data is injected into the positive and negative buses through injection capacitors, and the common-mode voltage amplitude at the corresponding frequencies is recorded sequentially. S43. Based on the phase of the injected sine wave, the phase change from the injection point to the detection point, and the phase relationship of the common-mode noise when the EUT is working normally, construct the fourth formula.

[0027] S44. Based on the common-mode noise amplitudes observed in S41 and S42, the common-mode noise amplitudes observed in S23 and S26, the amplitude ratio calculated in S32, the common-mode noise cancellation waveform amplitude calculated in S33, and the phase relationship between the injected wave and the measured common-mode noise, the fifth formula is constructed.

[0028] S45. Calculate the phase of the injected cancellation waveform at multiples of the first and second frequencies according to the fourth and fifth formulas, construct the sixth formula, and calculate the phase of the injected cancellation waveform at multiples of the switching frequency.

[0029] The fourth formula is: (4) The fifth formula is: (5) The sixth formula is: (6) In equations (4) to (6), α ( kf c )for kf c Inject the phase of the cancellation waveform at the frequency point. φ ( kf c )for kf c Common-mode noise phase at the frequency point θ ( kf c () represents the phase angle offset from the injection source to the common-mode noise detection point; Y rem ( kf c ) is the injection amplitude Y inj ( kf c The waveform obtained after cancellation was observed on LISN. kf c Common-mode noise voltage amplitude at the frequency point α test ( kf c )for kfc Inject any phase of the cancellation waveform at the frequency point.

[0030] More preferably, step S5 includes the following sub-steps: S51. Based on the amplitude and phase of the cancellation waveform obtained from S33 and S45, construct the seventh formula to obtain the injected cancellation waveform data.

[0031] S52. The injected cancellation waveform is stored in the digital controller and injected into the positive and negative buses through the single-ended DAC output to cancel common-mode noise.

[0032] The seventh formula is: (7) In equation (7), S 1( t ), S 2( t The switching frequencies are respectively: f c1 , f c2 The injection cancellation waveform within one cycle, N 1. N 2 represents the maximum achievable frequency band within the test band. f c1 , f c2 Multiples of, S ( t The waveform representing the common-mode noise cancellation injected during dual-frequency spread spectrum modulation PWM is shown below. M 1. M 2 represents the switching frequency. f c1 , f c2 The number of sub-cycles that repeat within a PWM cycle.

[0033] Preferably, the filtering method employs a digital active EMI filter circuit, which includes a LISN, an injection circuit, and a digital controller. The electrical connection of the digital active EMI filter circuit is as follows: the LISN is connected to the input terminal of the EUT under test, and the LISN is connected to the injection circuit to provide a stable impedance environment for electromagnetic interference measurement, ensuring stable power supply line impedance. The digital controller generates a dual-frequency spread-spectrum modulated PWM signal and also calculates, stores, and outputs common-mode noise cancellation waveform data. The injection circuit includes a series resistor and capacitor injected into the positive bus and a series resistor and capacitor injected into the negative bus, and a single-port output DAC. The DAC receives the common-mode noise cancellation waveform output by the digital controller, performs digital-to-analog conversion, and outputs an analog signal. The series resistor and capacitor on the positive and negative buses inject the analog common-mode noise cancellation waveform data output by the DAC into the positive and negative buses.

[0034] The beneficial effects of this invention are: In scenarios dominated by common-mode noise, this invention eliminates the need for detection circuits, thereby reducing costs and size. This invention can reduce common-mode noise by 41-45 dB in the low-frequency band and 34-40 dB in the high-frequency band of conducted interference testing. Attached Figure Description

[0035] Picture 1 This is a flowchart illustrating the EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform of the present invention. Picture 2 This is a flowchart illustrating step S1 of the present invention; Picture 3 This is a flowchart illustrating step S2 of the present invention; Picture 4 This is a flowchart illustrating step S3 of the present invention; Picture 5 This is a flowchart illustrating step S4 of the present invention; Picture 6 This is a flowchart illustrating step S5 of the present invention; Picture 7 This is a flowchart illustrating step S6 of the present invention; Picture 8 This is a schematic diagram of the structure of the present invention; Picture 9 This is a diagram showing the co-simulation spectrum effect of the present invention. Detailed Implementation

[0036] The related technologies of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] like Pictures 1-9 As shown, this embodiment provides a digital active EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveforms under conditions of missing common-mode noise phase observation. This digital active EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveforms can be applied to a terminal device, such as a mobile terminal like a mobile phone, desktop computer, personal digital assistant, laptop, tablet computer, or smartwatch. (Reference) Picture 1 As shown, the digital active EMI filtering method based on dual-frequency spread spectrum and dual-frequency recombined common-mode noise cancellation waveforms may include the following steps: Step S1: Select frequency 1 and frequency 2 as the constituent frequencies of the dual-frequency spread spectrum PWM.

[0038] Step S2: Use frequency 1 as the switching PWM frequency to enable the EUT to work normally, and obtain the common-mode noise amplitude data at multiples of that frequency; use frequency 2 as the switching PWM frequency to enable the EUT to work normally, and obtain the common-mode noise amplitude data at multiples of that frequency.

[0039] Step S3: Turn off the EUT's switching PWM signal, and output a sine wave with an amplitude of 1, arbitrary phase, and a frequency that is a multiple of the first and second frequencies through the DAC. The sine wave data is injected into the positive and negative buses through the injection capacitors to obtain the common-mode voltage amplitude at the frequency. Calculate the amplitude transformation ratio from the injection point to the common-mode noise observation point at the frequency and the amplitude of the injected cancellation waveform at the frequency.

[0040] Step S4: Use frequency 1 and frequency 2 as the switching PWM frequencies to enable the EUT to work normally. Output a sine wave with known amplitude and phase, and a frequency that is a multiple of frequency 1 or frequency 2 through the DAC. Inject the sine wave data into the positive and negative buses through the injection capacitors to obtain the common-mode voltage amplitude at the frequency and calculate the phase of the injected cancellation waveform at the frequency.

[0041] Step S5: Calculate the injection cancellation waveform data, output the cancellation waveform data synchronously with the dual-frequency spread spectrum PWM through the DAC, and inject the cancellation waveform data into the positive bus and negative bus through the injection capacitor to cancel the common mode voltage.

[0042] The aforementioned digital active EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform is suitable for scenarios dominated by common-mode noise. It can synchronously output with the DAC using a pre-calculated common-mode voltage cancellation waveform under a dual-frequency spread spectrum PWM signal, eliminating the need for detection circuitry and reducing both cost and size. Furthermore, as... Picture 9 As shown, common-mode noise can be reduced by 41-45 dB in the low-frequency band and by 34-40 dB in the high-frequency band of the conducted interference test band.

[0043] Below, we will refer to Picture 2 to Picture 7 The steps of the digital active EMI filtering method based on dual-frequency spread spectrum and dual-frequency recombined common-mode noise cancellation waveform described in this example embodiment will be explained in more detail.

[0044] In step S1, frequency 1 and frequency 2 are selected as the constituent frequencies of the dual-frequency spread spectrum PWM.

[0045] It should be noted that, in addition to the first and second frequencies, the relevant parameters of dual-frequency spread spectrum PWM also include the number of sub-cycles occupied by the first frequency and the number of sub-cycles occupied by the second frequency. These parameters are determined by iterative optimization after injecting the cancellation waveform, within the constraints imposed by the EUT operating conditions and performance indicators.

[0046] In one possible implementation, step S1 may further include the following sub-steps: In step S11, frequency one and frequency two are selected, and the first formula is constructed as the mathematical expression for dual-frequency spread spectrum PWM.

[0047] In step S12, the first formula is used to write a program in the digital controller as the final output dual-frequency spread spectrum PWM switching signal.

[0048] Furthermore, the first formula is: (1) in, P ( t () represents the expression for the dual-frequency spread spectrum modulation PWM signal within one cycle. f c1 is frequency number one. M 1 represents the number of sub-cycles at frequency number one. f c2 is the second frequency. M 2 represents the number of sub-cycles at frequency 2. D This represents the duty cycle.

[0049] In step S2, the first frequency is used as the switching PWM frequency to enable the EUT to work normally, and the common-mode noise amplitude data of multiples of that frequency is obtained; the second frequency is used as the switching PWM frequency to enable the EUT to work normally, and the common-mode noise amplitude data of multiples of that frequency is obtained.

[0050] It should be noted that common-mode noise amplitude data needs to be obtained by connecting to an EMI receiver via LISN.

[0051] In one possible implementation, step S2 may further include the following sub-steps: In step S21, the digital controller is programmed to generate a PWM waveform with a frequency of 1.

[0052] In step S22, the EUT is connected to a PWM waveform with frequency number one to enable it to work normally.

[0053] In step S23, the common-mode noise amplitude data at multiples of the first frequency are acquired by the EMI receiver connected via LISN.

[0054] It should be noted that, for example, frequency number one f c1=100kHz, then the sub-frequency multiples of the first frequency include 100kHz, 200kHz, 300kHz, etc.

[0055] In step S24, the digital controller is programmed to generate a PWM waveform with a frequency of frequency number two.

[0056] In step S25, the EUT is connected to a PWM waveform with frequency number two to enable it to work normally.

[0057] In step S26, the common-mode noise amplitude data at multiples of the second frequency are acquired by the EMI receiver connected via LISN.

[0058] Step S3: Turn off the EUT's switching PWM signal, and output a sine wave with an amplitude of 1, arbitrary phase, and a frequency that is a multiple of the first and second frequencies through the DAC. The sine wave data is injected into the positive and negative buses through the injection capacitors to obtain the common-mode voltage amplitude at the frequency. Calculate the amplitude transformation ratio from the injection point to the common-mode noise observation point at the frequency and the amplitude of the injected cancellation waveform at the frequency.

[0059] In one possible implementation, step S3 may further include the following sub-steps: In step S31, the switching PWM signal of the EUT is turned off, and a sine wave with an amplitude of 1, arbitrary phase, and a frequency that is a multiple of the first and second frequencies is output through the DAC. The sine wave data is injected into the positive and negative buses through the injection capacitor.

[0060] It should be noted that, for example, frequency number one f c1 =150kHz, frequency number two f c2 =200kHz, then the multiples of the first and second frequencies include 150kHz, 200kHz, 300kHz, 400kHz, 450kHz, etc.

[0061] In step S32, the common-mode voltage amplitude at the frequency is obtained, and a second formula is constructed based on the relationship between the injected sine wave amplitude and the common-mode voltage amplitude. The amplitude ratio from the injection point to the common-mode noise observation point at the frequency is calculated based on the second formula.

[0062] In step S33, based on the amplitude transformation ratio calculated in S32 and the common-mode voltage amplitude obtained in S23 and S26, a third formula is constructed, and the amplitude of the injection cancellation waveform at multiples of the first and second frequencies is calculated based on the third formula.

[0063] Furthermore, the second formula is: (2) in,G ( kf c )for kf c The amplitude variation from the injection source to the detection point at the frequency point Y mea ( kf c The common-mode voltage amplitude is obtained on the EMI receiver via LISN after injecting a sine wave. The third formula is: (3) in, Y inj ( kf c )for kf c The required common-mode cancellation waveform amplitude at the frequency point, A ( kf c When the EUT is working properly kf c The common-mode noise amplitude measured at the specified frequency.

[0064] It should be noted that, kf c The frequency point is the frequency point where the first frequency and the second frequency are multiples of each other. k =1,2,... , f max To test the upper limit frequency of the frequency band, f c = f c1 or f c2 The amplitude ratio from the injection point to the common-mode noise observation point at each multiple of the switching frequency is calculated using the second formula; the required common-mode cancellation waveform amplitude at each multiple of the switching frequency is calculated using the third formula.

[0065] Step S4: Use frequency 1 and frequency 2 as the switching PWM frequencies to enable the EUT to work normally. Output a sine wave with known amplitude, arbitrary phase, and frequency that is a multiple of the current PWM frequency through the DAC. Inject the sine wave data into the positive and negative buses through the injection capacitors to obtain the common-mode voltage amplitude at the current output frequency of the DAC and calculate the phase of the injected cancellation waveform at the current output frequency of the DAC.

[0066] It should be noted that the amplitude of the sine wave output by the DAC, with known amplitude, known phase, and a frequency that is a multiple of the current PWM frequency, is the value in the third formula. Y inj ( kfc The phase is any given value.

[0067] In one possible implementation, step S4 may further include the following sub-steps: In step S41, frequency 1 is used as the switching PWM frequency to enable the EUT to operate normally, and the amplitude is sequentially output through the DAC as calculated in S33. Y inj ( kf c1 A sine wave with an arbitrarily given phase and a frequency that is a multiple of the first frequency is generated. The sine wave data is injected into the positive and negative bus through injection capacitors, and the common-mode voltage amplitude at the corresponding frequency is recorded in sequence.

[0068] In step S42, the second frequency is used as the switching PWM frequency to enable the EUT to operate normally, and the amplitude is sequentially output through the DAC as calculated in S33. Y inj ( kf c2 A sine wave with an arbitrarily given phase and a frequency that is a multiple of the second frequency is generated. The sine wave data is injected into the positive and negative bus through the injection capacitor, and the common-mode voltage amplitude at the corresponding frequency is recorded in sequence.

[0069] In step S43, a fourth formula is constructed based on the phase of the injected sine wave, the phase change from the injection point to the detection point, and the phase relationship of the common-mode noise when the EUT is operating normally.

[0070] In step S44, a fifth formula is constructed based on the common-mode noise amplitudes observed in S41 and S42, the common-mode noise amplitudes observed in S23 and S26, the amplitude ratio calculated in S32, the common-mode noise cancellation waveform amplitude calculated in S33, and the phase relationship between the injected wave and the measured common-mode noise.

[0071] In step S45, the phase of the injected cancellation waveform at multiples of the first and second frequencies is calculated according to the fourth and fifth formulas, and the sixth formula is constructed to calculate the phase of the injected cancellation waveform at multiples of the switching frequency.

[0072] Furthermore, the fourth formula is: (4) in, α ( kf c) is kf Inject the phase of the cancellation waveform at frequency c. φ ( kf c) is kf Common-mode noise phase at frequency c θ ( kfc) is the phase angle offset from the injection source to the common-mode noise detection point; The fifth formula is: (5) in, Y rem ( kf c ) is the injection amplitude Y inj ( kf c The waveform obtained after cancellation was observed on LISN. kf c Common-mode noise voltage amplitude at the frequency point α test ( kf c )for kf c Inject any phase of the cancellation waveform at the frequency point; The sixth formula is: (6) Step S5: Calculate the injection cancellation waveform data, output the cancellation waveform data synchronously with the dual-frequency spread spectrum PWM through the DAC, and inject the cancellation waveform data into the positive bus and negative bus through the injection capacitor to cancel the common mode voltage.

[0073] It should be noted that common-mode noise is the in-phase interference between the positive / negative busbar and the grounding protection line, while differential-mode noise is the potential difference between the positive and negative busbars. By simultaneously injecting signals of the same amplitude and phase into the positive / negative busbars, common-mode noise can be canceled without introducing additional differential-mode noise.

[0074] In one possible implementation, step S5 may further include the following sub-steps: In step S51, based on the amplitude and phase of the cancellation waveform obtained in S33 and S45, the seventh formula is constructed to obtain the injected cancellation waveform data.

[0075] In step S52, the injected cancellation waveform is stored in the digital controller and injected into the positive and negative buses through the output of the single-ended DAC to cancel common-mode noise.

[0076] Furthermore, the amplitude and phase of the injection cancellation waveform at each multiple of the switching frequency are superimposed using the seventh formula, which is: (7) in, S 1( t (The switching frequency is...) f c1 The injection cancellation waveform within one cycle, N1 represents the maximum achievable frequency band within the test band. f c1 Multiples of; S 2( t (The switching frequency is...) f c2 The injection cancellation waveform within one cycle, N 2 represents the maximum achievable frequency band within the test band. f c2 Multiples of; S ( t This represents the common-mode noise cancellation waveform injected during dual-frequency spread spectrum modulation PWM. M 1 represents the switching frequency. f c1 The number of sub-cycles that repeat within a PWM cycle; M 2 represents the switching frequency. f c2 The number of sub-cycles that repeat within a PWM cycle.

[0077] It should be noted that the final injection cancellation waveform is... S ( t The output of ) should be synchronized with the starting point of the dual-frequency spread spectrum PWM in step S1.

[0078] After step S5, the method further includes: Step S6: Measure the common-mode noise on the LISN, and iteratively adjust the number of sub-cycles occupied by the first frequency and the number of sub-cycles occupied by the second frequency in the dual-frequency spread spectrum PWM within the allowable range of EUT operating conditions until the sub-cycle number parameter that minimizes the common-mode noise is found.

[0079] In one possible implementation, S6 may further include the following sub-steps: In step S61, within the allowable range of EUT operating conditions, a set of sub-cycles occupied by frequency one and sub-cycles occupied by frequency two are selected.

[0080] In step S62, the common-mode voltage on the LISN is measured and recorded.

[0081] In step S63, the number of sub-cycles occupied by frequency one or frequency two is changed within the allowable range of EUT operating conditions. In step S64, repeat S62 and S63 to find the number of sub-cycles occupied by frequency 1 and frequency 2 corresponding to the minimum common-mode noise within the allowable range of EUT operating conditions.

[0082] It should be noted that the allowable range of EUT operating conditions includes indicators such as acceptable ripple size and efficiency, which should be determined based on the specific circumstances of the EUT.

[0083] Furthermore, this embodiment also provides a digital active EMI filter circuit based on dual-frequency spread spectrum and dual-frequency recombined common-mode noise cancellation waveforms, used to perform the above-described digital active EMI filter method based on dual-frequency spread spectrum and dual-frequency recombined common-mode noise cancellation waveforms. (Reference) Picture 8 As shown, the circuit may include a LISN, an injection circuit, and a digital controller; The LISN is connected to the input terminal of the EUT under test and to the injection circuit to provide a stable impedance environment for electromagnetic interference measurement, thereby stabilizing the impedance of the power supply line. The digital controller is used to generate dual-frequency spread spectrum modulation (PWM) signals, and to calculate, store, and output common-mode noise cancellation waveform data; The injection circuit includes a series resistor and capacitor injected into the positive bus and a series resistor and capacitor injected into the negative bus, as well as a single-port output DAC. The DAC is used to receive the common-mode noise cancellation waveform output by the digital controller and perform digital-to-analog conversion before outputting an analog signal. The series resistor and capacitor on the positive and negative buses are used to inject the analog common-mode noise cancellation waveform data output by the DAC into the positive and negative buses.

[0084] It should be noted that, as Picture 8 As shown, the LISN includes a low-pass filter formed by resistors, inductors, and capacitors connected in series with the power supply, and a load resistor, used for impedance matching to ensure the accuracy of EMI measurements. The injection circuit includes a positive bus injection capacitor. C 1. Injection capacitor into the negative bus C 2. For the DAC, one end of the positive bus injection capacitor is connected to the positive bus, and the other end is connected to the DAC output terminal; one end of the negative bus injection capacitor is connected to the negative bus, and the other end is connected to the DAC output terminal; the DAC output is injected with cancellation waveform data.

[0085] In summary, this invention can reduce common-mode noise by 41-45 dB in the low-frequency range and 34-40 dB in the high-frequency range of the conducted interference test band without the need for a detection circuit. This invention is suitable for scenarios where common-mode noise is dominant, and can achieve common-mode suppression while reducing size. Therefore, this invention has broad application prospects in the field of digital active EMI filtering.

[0086] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. An EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform, characterized in that, Includes the following steps: Step S1: Select frequency 1 and frequency 2 as the constituent frequencies of the dual-frequency spread spectrum PWM; Step S2: Use frequency 1 as the switching PWM frequency to enable the EUT to work normally and obtain common-mode noise amplitude data at multiples of frequency 1; use frequency 2 as the switching PWM frequency to enable the EUT to work normally and obtain common-mode noise amplitude data at multiples of frequency 2. Step S3: Turn off the EUT's switching PWM signal, and output a sine wave with an amplitude of 1, arbitrary phase, and frequency that is a multiple of the first and second frequencies through the DAC. The sine wave data is injected into the positive and negative buses through the injection capacitors to obtain the common-mode voltage amplitude at the current output frequency of the DAC. Calculate the amplitude transformation ratio from the injection point to the common-mode noise observation point at the current output frequency of the DAC and the amplitude of the injected cancellation waveform at the frequency. Step S4: Use frequency 1 and frequency 2 as the switching PWM frequencies to make the EUT work normally. Output a sine wave with known amplitude, known phase, and frequency that is a multiple of the current PWM frequency through the DAC. Inject the sine wave data into the positive and negative buses through the injection capacitors to obtain the common-mode voltage amplitude at the current output frequency of the DAC and calculate the phase of the injected cancellation waveform at the current output frequency of the DAC. Step S5: Calculate the injection cancellation waveform data, output the cancellation waveform data synchronously with the dual-frequency spread spectrum PWM through the DAC, and inject the cancellation waveform data into the positive bus and negative bus through the injection capacitor to cancel the common mode voltage.

2. The EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform according to claim 1, characterized in that, Step S5 is followed by step S6, which involves measuring the common-mode noise on the LISN and iteratively adjusting the number of sub-cycles occupied by the first frequency and the second frequency in the dual-frequency spread spectrum PWM within the allowable range of the EUT operating conditions until the sub-cycle number parameter that minimizes the common-mode noise is found.

3. The EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform according to claim 2, characterized in that, Step S6 includes the following sub-steps: S61. Within the allowable range of EUT operating conditions, select a set of sub-cycles occupied by frequency 1 and sub-cycles occupied by frequency 2. S62. Measure and record the common-mode voltage on the LISN; S63. Within the allowable range of EUT operating conditions, change the number of sub-cycles occupied by frequency one or frequency two. S64. Repeat S62 and S63 to find the number of sub-cycles occupied by frequency 1 and frequency 2 corresponding to the minimum common-mode noise within the allowable range of EUT operating conditions.

4. The EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform according to claim 1, characterized in that, Step S1 includes the following sub-steps: S11. Select frequency 1 and frequency 2, and construct the first formula as the mathematical expression for dual-frequency spread spectrum PWM; S12. Using the first formula, write a program in the digital controller as the final output dual-frequency spread spectrum PWM switching signal; The first formula is: （1） In equation (1), P ( t () represents the expression for the dual-frequency spread spectrum modulation PWM signal within one cycle. f c1 Frequency number one. M 1 represents the number of sub-cycles at frequency number one. f c2 It is frequency number two. M 2 represents the number of sub-cycles at frequency 2. D Here, n represents the duty cycle, t represents the sub-cycle number, and t represents time.

5. The EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform according to claim 4, characterized in that, Step S2 includes the following sub-steps: S21. Program the digital controller to generate a PWM waveform with frequency number one. S22. Apply a PWM waveform with frequency 1 to the EUT to make the EUT work normally. In S23, the common-mode noise amplitude data of multiples of the first frequency is obtained by the EMI receiver connected via LISN; In S24, the digital controller is programmed to generate a PWM waveform with a frequency of frequency two. In S25, the EUT is connected to a PWM waveform with frequency number two to make the EUT work normally; In S26, the EMI receiver connected via LISN acquires common-mode noise amplitude data at multiples of the second frequency.

6. The EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform according to claim 5, characterized in that, Step S3 includes the following sub-steps: S31. Turn off the EUT's switching PWM signal, and output a sine wave with an amplitude of 1, arbitrary phase, and frequency that is a multiple of the first and second frequencies through the DAC. Inject the sine wave data into the positive and negative buses through the injection capacitors. S32. Obtain the common-mode voltage amplitude at the DAC output frequency. Construct a second formula based on the relationship between the injected sine wave amplitude and the common-mode voltage amplitude. Calculate the amplitude ratio from the injection point to the common-mode noise observation point at the frequency based on the second formula. S33. Based on the amplitude transformation ratio calculated in step S32 and the common-mode voltage amplitude obtained in steps S23 and S26, construct the third formula, and calculate the amplitude of the first frequency and the second frequency multiple injection cancellation waveform according to the third formula. The second formula is: （2） In equation (2), G ( kf c )for kf c The amplitude variation from the injection source to the detection point at the frequency point Y mea ( kf c The common-mode voltage amplitude is obtained on the EMI receiver via LISN after injecting a sine wave. The third formula is: （3） In equation (3), Y inj ( kf c )for kf c The required common-mode cancellation waveform amplitude at the frequency point, A ( kf c When the EUT is working properly kf c The common-mode noise amplitude measured at the specified frequency.

7. The EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform according to claim 6, characterized in that, Step S4 includes the following sub-steps: S41. Using frequency 1 as the switching PWM frequency, the EUT is made to work normally, and the amplitude is sequentially output through the DAC to the value calculated in step S33. Y inj ( kf c1 A sine wave with an arbitrarily given phase and a frequency that is a multiple of the first frequency is generated. The sine wave data is injected into the positive and negative bus through an injection capacitor, and the common-mode voltage amplitude at the corresponding frequency is recorded in sequence. S42. Using frequency 2 as the switching PWM frequency to ensure normal operation of the EUT, the DAC sequentially outputs amplitudes calculated in S33. Y inj ( kf c2 A sine wave with an arbitrarily given phase and a frequency that is a multiple of the second frequency is generated. The sine wave data is injected into the positive and negative bus through an injection capacitor, and the common-mode voltage amplitude at the corresponding frequency is recorded in sequence. S43. Based on the phase of the injected sine wave, the phase change from the injection point to the detection point, and the phase relationship of the common-mode noise when the EUT is working normally, construct the fourth formula; S44. Construct the fifth formula based on the common-mode noise amplitude observed in S41 and S42, the common-mode noise amplitude observed in S23 and S26, the amplitude ratio calculated in S32, the common-mode noise cancellation waveform amplitude calculated in S33, and the phase relationship between the injected wave and the measured common-mode noise. S45. Calculate the phase of the injected cancellation waveform at multiples of the first and second frequencies according to the fourth and fifth formulas, construct the sixth formula, and calculate the phase of the injected cancellation waveform at multiples of the switching frequency. The fourth formula is: （4） The fifth formula is: （5） The sixth formula is: （6） In equations (4) to (6), α ( kf c )for kf c Inject the phase of the cancellation waveform at the frequency point. φ ( kf c )for kf c Common-mode noise phase at the frequency point θ ( kf c () represents the phase angle offset from the injection source to the common-mode noise detection point; Y rem ( kf c ) is the injection amplitude Y inj ( kf c The waveform obtained after cancellation was observed on LISN. kf c Common-mode noise voltage amplitude at the frequency point α test ( kf c )for kf c Inject any phase of the cancellation waveform at the frequency point.

8. The EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform according to claim 7, characterized in that, Step S5 includes the following sub-steps: S51. Based on the amplitude and phase of the cancellation waveform obtained in S33 and S45, construct the seventh formula to obtain the injected cancellation waveform data. S52. Store the injected cancellation waveform in the digital controller, and inject it into the positive and negative buses through the single-ended DAC output to cancel common-mode noise; The seventh formula is: （7） In equation (7), S 1( t ), S 2( t The switching frequencies are respectively: f c1 , f c2 The injection cancellation waveform within one cycle, N 1. N 2 represents the maximum achievable frequency band within the test band. f c1 , f c2 Multiples of, S ( t The waveform representing the common-mode noise cancellation injected during dual-frequency spread spectrum modulation PWM is shown below. M 1. M 2 represents the switching frequency. f c1 , f c2 The number of sub-cycles that repeat within a PWM cycle.

9. The EMI filtering method based on dual-frequency spread spectrum and dual-frequency reconstructed common-mode noise cancellation waveform according to claim 1, characterized in that, The filtering method employs a digital active EMI filter circuit, which includes a LISN, an injection circuit, and a digital controller. The electrical connection of the digital active EMI filter circuit is as follows: the LISN is connected to the input terminal of the EUT under test, and the LISN is connected to the injection circuit to provide a stable impedance environment for electromagnetic interference measurement, thereby stabilizing the impedance of the power supply line. The digital controller is used to generate dual-frequency spread spectrum modulation (PWM) signals. It is also used to calculate, store, and output common-mode noise cancellation waveform data. The injection circuit includes a series resistor and capacitor injected into the positive bus and a series resistor and capacitor injected into the negative bus, and a single-port output DAC; the DAC is used to receive the common-mode noise cancellation waveform output by the digital controller, and output it as an analog signal after digital-to-analog conversion; the series resistor and capacitor of the positive and negative buses are used to inject the analog common-mode noise cancellation waveform data output by the DAC into the positive and negative buses.

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