Common-mode and differential-mode simultaneous suppression active impedance shaping EMI filter and design method thereof

Abstract

The invention discloses an active impedance shaping EMI filter involving common-mode and differential-mode simultaneous suppression, which comprises a high-pass impedance module I. The high-pass impedance module I and a band-pass impedance module I are connected in parallel to form a low-impedance branch I, and the low-impedance branch I is connected in parallel between an L line and a PE line; the high-pass impedance module II and the band-pass impedance module II are connected in parallel to form a low-impedance branch II, and the low-impedance branch II is connected in parallel between the N line and the PE line. The invention also discloses a design method of the active impedance shaping EMI filter capable of simultaneously inhibiting the common mode and the differential mode. The problem that low equivalent impedance requirements of common-mode interference and differential-mode interference are difficult to meet at the same time when a capacitor is used as a filter at present is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic compatibility of power electronic systems, and relates to an EMI filter with active impedance shaping for simultaneous common-mode and differential-mode suppression. The present invention also relates to a design method for an EMI filter with active impedance shaping for simultaneous common-mode and differential-mode suppression. Background Art

[0002] The widespread use of wide bandgap semiconductor devices represented by silicon carbide and gallium nitride has led to continuous increases in the switching frequency and power density of switching power converters, resulting in more complex conducted electromagnetic interference in switching power converters. Capacitors are used as passive EMI (Electro Magnetic Interference) filters, mainly by providing a low-impedance path to suppress conducted electromagnetic interference. However, the impedance of a capacitor varies regularly with its own capacitance value, so it is difficult to perform impedance shaping in any frequency band to cope with the complex changing electromagnetic environment. At the same time, when suppressing the conducted electromagnetic interference of a switching power converter, it is necessary to consider both common-mode interference and differential-mode interference. Without using a choke inductor, which has a low power density, it is difficult for a capacitor to simultaneously meet the low equivalent impedance requirements of common-mode interference and differential-mode interference. Therefore, it is necessary to consider the impedance matching of filters for the two types of interference to achieve low-impedance shaping of the capacitor. Summary of the Invention

[0003] The purpose of the present invention is to provide an EMI filter with active impedance shaping for simultaneous common-mode and differential-mode suppression, which solves the problem that it is difficult to simultaneously meet the low equivalent impedance requirements of common-mode interference and differential-mode interference when using a capacitor as a filter at present.

[0004] Another purpose of the present invention is to provide a design method for an EMI filter with active impedance shaping for simultaneous common-mode and differential-mode suppression.

[0005] The first technical solution adopted by the present invention is an EMI filter with active impedance shaping for simultaneous common-mode and differential-mode suppression, which includes a first high-pass impedance module. The first high-pass impedance module and a first band-pass impedance module are connected in parallel to form a first low-impedance branch, and the first low-impedance branch is connected in parallel between the L line and the PE line.

[0006] It further includes a second high-pass impedance module. The second high-pass impedance module and a second band-pass impedance module are connected in parallel to form a second low-impedance branch, and the second low-impedance branch is connected in parallel between the N line and the PE line.

[0007] The characteristics of the first technical solution of the present invention also lie in:

[0008] The second high-pass impedance module has the same structure as the first high-pass impedance module. The first high-pass impedance module includes a first high-pass impedance shaping circuit, and the first high-pass impedance shaping circuit is respectively connected to an injection circuit and an impedance cancellation circuit.

[0009] The band - pass impedance module two has the same structure as the band - pass impedance module one. The band - pass impedance module one includes a band - pass impedance shaping circuit one, and the band - pass impedance shaping circuit one is respectively connected to an injection circuit and an impedance cancellation circuit.

[0010] The injection circuit includes an injection resistor R in , the injection resistor R in and an injection capacitor C in to form a high - pass filter.

[0011] The impedance cancellation circuit includes a cancellation resistor R io , the cancellation resistor R io and a cancellation capacitor C io to form a high - pass filter.

[0012] The high - pass impedance shaping circuit one includes an operational amplifier OPA. The positive - feedback branch of the operational amplifier OPA is successively connected to a high - pass shaping resistor R1 and a high - pass shaping capacitor C2, and the positive - feedback branch of the operational amplifier OPA is also connected to the cancellation resistor R io ; the negative - feedback branch of the operational amplifier OPA is respectively connected to another high - pass shaping resistor R1 and the injection resistor R in .

[0013] The band - pass impedance shaping circuit one includes an operational amplifier OPA. The positive - feedback branch of the operational amplifier OPA is connected to a band - pass shaping resistor R3 and the cancellation resistor R io , the negative - feedback branch of the operational amplifier OPA is respectively connected to another band - pass shaping capacitor C3 and the injection resistor R in , and the band - pass shaping capacitor C3 is respectively in parallel with a band - pass shaping inductor L3 and another band - pass shaping resistor R3.

[0014] The second technical solution adopted by the present invention is a design method of an active impedance - shaping EMI filter with common - mode and differential - mode simultaneous suppression. The design requirements of the injection circuit are as follows:

[0015] When the frequency exceeds the starting frequency of 150 kHz of conducted electromagnetic interference, according to the impedance characteristics of the capacitor, the impedance of the injection circuit is only related to the injection resistor R in , and the impedance of the injection capacitor C in is negligible. At this time, according to Ohm's law, the resistance value of the injection resistor R in is:

[0016]

[0017] Among them, U EMI1 is the fundamental - harmonic voltage of the switching frequency of the switched - mode power converter; U EMI3 is the third - harmonic voltage of the switching frequency of the switched - mode power converter; U EMI5is the fifth harmonic voltage of the switching frequency of the switching power converter; I OPA is the maximum input current of the operational amplifier;

[0018] According to Joule's law, the injection resistor R in The selected rated power P Rin is:

[0019]

[0020] The injection resistor R in and the injection capacitor C in The cut-off frequency f0 of the high-pass filter composed of the series connection is designed according to the impedance shaping frequency f of the active impedance shaping EMI filter s The formula is:

[0021]

[0022] According to formula (1) and formula (3), the capacitance value of the injection capacitor C in is:

[0023]

[0024] Among them, I OPA is the maximum input current of the operational amplifier OPA;

[0025] The injection capacitor C in The rated voltage U Cin is:

[0026]

[0027] Among them, U IN is the voltage on the input side of the switching power converter.

[0028] The design requirements of the impedance cancellation circuit are as follows:

[0029] The impedance cancellation circuit is a high-pass filter composed of the cancellation resistor R io and the cancellation capacitor C io in series, generating a negative impedance equal to the amplitude of the impedance of the injection circuit in the electromagnetic interference frequency band, so that the impedance of the entire EMI filter is zero in the electromagnetic interference frequency band. At this time, the impedance Z of the EMI filter AEF The formula is:

[0030]

[0031] Among them, α is the impedance shaping coefficient;

[0032] To make the sum of the impedances of the impedance cancellation circuit and the injection circuit zero, the cut-off frequencies of the impedance cancellation circuit and the injection circuit should be the same. The formula for the cut-off frequency f0 is:

[0033]

[0034] According to Formula (6) and Formula (7), the formula for the cancellation capacitor C io is:

[0035]

[0036] According to Formula (6) and Formula (7), the formula for the cancellation resistor R io is:

[0037]

[0038] The design requirements of the first high-pass impedance shaping circuit are as follows:

[0039] Considering the parasitic resistance R ESR and parasitic inductance L ESL of the high-pass shaping capacitor C2, the formula for the impedance shaping coefficient α is:

[0040]

[0041] wherein, R1 is the high-pass shaping resistor; C2 is the high-pass shaping capacitor; L ESL is the parasitic inductance of the high-pass shaping capacitor C2; R ESR is the parasitic resistance of the high-pass shaping capacitor C2;

[0042] For the high-pass impedance shaping circuit, the high-pass impedance shaping frequency f s is:

[0043]

[0044] According to Formula (10) and Formula (11), the formula for the high-pass shaping resistor R1 is:

[0045]

[0046] According to Formula (10) and Formula (11), the formula for the high-pass shaping capacitor C2 is:

[0047]

[0048] The design requirements of the first band-pass impedance shaping circuit are as follows:

[0049] The band-pass impedance shaping circuit 1 contains a band-pass shaping capacitor C3 and a band-pass shaping inductor L3. Therefore, according to the frequency characteristics of the LC filter, the center frequency f of the band-pass impedance shaping circuit 1 c has the formula:

[0050]

[0051] where, L3 is the band-pass shaping inductor; C3 is the band-pass shaping capacitor;

[0052] According to the design principle of the conduction EMI band-pass filtering frequency band, another calculation formula for the center frequency f of the band-pass impedance shaping circuit 1 c is:

[0053]

[0054] where, f low is the lower limit frequency of the filtering frequency band; BW is the conduction EMI filtering frequency band; f up is the upper limit frequency of the filtering frequency band;

[0055] Based on the impedance shaping principle of the EMI filter, the calculation formula for the impedance shaping coefficient α of the band-pass impedance shaping circuit 1 is:

[0056]

[0057] where, R3 is the band-pass shaping resistor;

[0058] In order to ensure that the impedance shaping coefficient α of the band-pass impedance shaping circuit 1 is maintained between 0 and 1, the relationship between the band-pass shaping resistor R3, the band-pass shaping capacitor C3 and the band-pass shaping inductor L3 is:

[0059]

[0060] where, k is the multiple of the inductance resistance value at the center frequency of the filtering frequency band;

[0061] According to formulas (14) to (17), the design formula for the band-pass shaping capacitor C3 is obtained as:

[0062]

[0063] According to formulas (14) to (17), the design formula for the band-pass shaping inductor L3 is obtained:

[0064]

[0065] According to formulas (14) to (17), the design formula for the band-pass shaping resistor R3 is obtained:

[0066]

[0067] The beneficial effects of the present invention are as follows. The present invention takes into account the impedance matching characteristics of common-mode and differential-mode electromagnetic interference filters, and designs a high-power-density EMI filter that can suppress both common-mode and differential-mode interference simultaneously. In the design method of the filter of the present invention, by taking advantage of the characteristic that the capacitor provides a low-impedance path for filtering in the electromagnetic interference frequency band and considering the impedance cancellation characteristic of the impedance cancellation circuit, an ultra-low impedance in a specific electromagnetic interference frequency band can be achieved, thereby improving the filtering ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is the circuit topology diagram of the EMI filter with active impedance shaping for simultaneous suppression of common-mode and differential-mode of the present invention;

[0069] Figure 2 is the output impedance curve diagram of the EMI filter with active impedance shaping for simultaneous suppression of common-mode and differential-mode of the present invention;

[0070] Figure 3 is the measurement waveform diagram of the common-mode conducted EMI suppression of the switching power converter of the EMI filter with active impedance shaping for simultaneous suppression of common-mode and differential-mode of the present invention;

[0071] Figure 4 is the measurement waveform diagram of the differential-mode conducted EMI suppression of the switching power converter of the EMI filter with active impedance shaping for simultaneous suppression of common-mode and differential-mode of the present invention.

[0072] Figure 5 is the actual impedance measurement waveform diagram of the EMI filter with active impedance shaping for simultaneous suppression of common-mode and differential-mode of the present invention.

[0073] In the figure, 1. power grid / power supply, 2. switching power converter, 4. high-pass impedance module one, 5. band-pass impedance module one, 6. high-pass impedance module two, 7. band-pass impedance module two, 8. injection circuit, 9. impedance cancellation circuit, 10. high-pass impedance shaping circuit one, 11. band-pass impedance shaping circuit one, 12. high-pass impedance shaping circuit two, 13. band-pass impedance shaping circuit two. DETAILED DESCRIPTION OF THE INVENTION

[0074] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0075] Embodiment 1

[0076] The EMI filter with active impedance shaping for simultaneous suppression of common-mode and differential-mode of the present invention, as Figure 1As shown, it includes a high-pass impedance module 1-4, a band-pass impedance module 1-5, a high-pass impedance module 2-6, and a band-pass impedance module 2-7. Among them, the high-pass impedance module 1-4 is composed of an injection circuit 8, an impedance cancellation circuit 9, and a high-pass impedance shaping circuit 1-10; the band-pass impedance module 1-5 is composed of an injection circuit 8, an impedance cancellation circuit 9, and a band-pass impedance shaping circuit 1-11; the high-pass impedance module 2-6 is composed of an injection circuit 8, an impedance cancellation circuit 9, and a high-pass impedance shaping circuit 2-12; the band-pass impedance module 2-7 is composed of an injection circuit 8, an impedance cancellation circuit 9, and a band-pass impedance shaping circuit 2-13.

[0077] Embodiment 2

[0078] The common-mode electromagnetic interference generated by the switching power converter 2 is the sum of the interference between the L line and the PE line and the interference between the N line and the PE line. The high-pass impedance module 1-4 and the band-pass impedance module 1-5 are connected in parallel to form a low-impedance branch 1, which is connected in parallel between the L line and the PE line, and can suppress the interference between the L line and the PE line; the high-pass impedance module 2-6 and the band-pass impedance module 2-7 are connected in parallel to form a low-impedance branch 2, which is connected in parallel between the N line and the PE line, and can suppress the interference between the N line and the PE line.

[0079] The differential-mode electromagnetic interference generated by the switching power converter 2 is the interference between the L line and the N line. The parallel low-impedance branch 1 composed of the high-pass impedance module 1-4 and the band-pass impedance module 1-5 is connected in series with the parallel low-impedance branch 2 composed of the high-pass impedance module 2-6 and the band-pass impedance module 2-7, and a series low-impedance path for suppressing the interference between the L line and the N line can be obtained. Therefore, the active impedance shaping EMI filter of the present invention can simultaneously suppress the common-mode and differential-mode interference generated by the switching power converter.

[0080] Embodiment 3

[0081] The injection circuit 8 includes an injection resistor R in and an injection capacitor C in . The injection resistor R in and the injection capacitor C in form a high-pass filter to isolate low-frequency non-electromagnetic interference signals from entering the EMI filter.

[0082] Embodiment 4

[0083] The impedance cancellation circuit 9 includes a cancellation resistor R io and a cancellation capacitor C io . The impedance cancellation circuit 9 forms an equivalent negative impedance opposite to the impedance of the injection circuit 8, so that the impedance of the entire EMI filter (equal to the sum of the impedance of the injection circuit 8 and the impedance of the impedance cancellation circuit 9) is close to zero in the electromagnetic interference frequency band, achieving an ultra-low impedance. Therefore, the cancellation resistor R io and the cancellation capacitor C io will be combined with the injection resistor Rin and the injection capacitor C in have the same circuit structure.

[0084] Embodiment 5

[0085] The high-pass impedance shaping circuit 10 includes two high-pass shaping resistors R1, a high-pass shaping capacitor C2, and an operational amplifier OPA. One high-pass shaping resistor R1 is in the positive feedback branch of the operational amplifier OPA, and the other high-pass shaping resistor R1 is in the negative feedback branch of the operational amplifier OPA. By the ratio of the impedance of the negative feedback branch of the operational amplifier OPA to the impedance of the positive feedback branch of the operational amplifier OPA, the impedance shaping coefficient α is obtained to adjust the impedance value of the impedance cancellation circuit 9. Since there is a resonance point a between the high-pass shaping resistor R1 and the high-pass shaping capacitor C2 in the positive feedback branch of the operational amplifier OPA, the impedance shaping coefficient α is 1 at frequencies higher than the resonance frequency at point a, and the impedance shaping coefficient α is 0 at frequencies lower than the resonance frequency at point a. Furthermore, the impedance of the impedance cancellation circuit 9 in the frequency band higher than the resonance frequency at point a is equal to the impedance of the injection circuit 8, and the impedance in the frequency band lower than the resonance frequency at point a approaches zero, achieving the high-pass impedance shaping of the EMI filter. The high-pass impedance shaping circuit 12 and the high-pass impedance shaping circuit 10 have the same circuit structure and implementation functions.

[0086] Embodiment 6

[0087] The band-pass impedance shaping circuit 11 includes two band-pass shaping resistors R3, a band-pass shaping capacitor C3, a band-pass shaping inductor L3, and an operational amplifier OPA. One band-pass shaping resistor R3 is in the positive feedback branch of the operational amplifier OPA, and the other high-pass shaping resistor R3 is in the negative feedback branch of the operational amplifier OPA. By the ratio of the impedance of the negative feedback branch of the operational amplifier OPA to the impedance of the positive feedback branch of the operational amplifier OPA, the impedance shaping coefficient α is obtained to adjust the impedance value of the impedance cancellation circuit 9. Since there is a resonance point between the band-pass shaping resistor R3 and the band-pass shaping capacitor C3 in the negative feedback branch of the operational amplifier OPA and between the band-pass shaping resistor R3 and the band-pass shaping inductor L3 in the negative feedback branch of the operational amplifier OPA, the impedance shaping coefficient α is 1 within these two resonance frequency ranges, and the impedance shaping coefficient α is 0 outside these two resonance frequency ranges. Furthermore, the impedance of the impedance cancellation circuit 9 in the frequency band between the resonance frequencies is equal to the impedance of the injection circuit 8, and the impedance outside the resonance frequencies approaches zero, achieving the band-pass impedance shaping of the EMI filter. The band-pass impedance shaping circuit 13 and the band-pass impedance shaping circuit 11 have the same circuit structure and implementation functions.

[0088] The impedance shaping curve diagram of the EMI filter with common-mode and differential-mode simultaneous suppression and active impedance shaping of the present invention is as Figure 2 shown, including the output impedance curve Z of the high-pass impedance module 4GT 1. The output impedance curve Z of the band - pass impedance module 1 - 5 DT and the output impedance curve Z of the parallel low - impedance branch 1 - 1 formed by the high - pass impedance module 1 - 4 and the band - pass impedance module 1 - 5 LPE . By paralleling the output impedance of the high - pass impedance module 1 - 4 and the output impedance of the band - pass impedance module 1 - 5, the output impedance of the parallel low - impedance branch 1 - 1 formed by the high - pass impedance module 1 - 4 and the band - pass impedance module 1 - 5 is obtained. The band - pass impedance module 1 - 5 helps the high - pass impedance module 1 - 4 reduce the output impedance at the initial stage of the electromagnetic interference frequency band. The output impedance curves of the high - pass impedance module 2 - 6, the band - pass impedance module 2 - 7, and the parallel low - impedance branch 2 - 1 formed by the high - pass impedance module 2 - 6 and the band - pass impedance module 2 - 7 are the same as Figure 3 the curve shown in

[0089] . The active impedance - shaping EMI filter is located between the power grid / power supply 1 and the switched - mode power converter 2. The high - pass impedance module 1 - 4 and the band - pass impedance module 1 - 5 are paralleled between the L - line and the PE - line, and the high - pass impedance module 2 - 6 and the band - pass impedance module 2 - 7 are paralleled between the N - line and the PE - line.

[0090] The high-pass impedance module 1-4 consists of an injection circuit 8, an impedance cancellation circuit 9, and a high-pass impedance shaping circuit 1-10. The EMI current flowing through the injection circuit 8 enters from the negative input terminal of the operational amplifier OPA of the high-pass impedance shaping circuit 1-10, and then flows out from the positive input terminal of the operational amplifier OPA of the high-pass impedance shaping circuit 1-10 and enters the impedance cancellation circuit 9. When the amplitude of the EMI current flowing out of the operational amplifier OPA is equal to that of the EMI current flowing into the operational amplifier OPA and the phases are opposite, the sum of the voltages of the injection circuit 8 and the impedance cancellation circuit 9 can be zero, and it is considered that the impedance of the high-pass impedance module 1-4 at this time is zero, that is, the impedance of the impedance cancellation circuit 9 and the injection circuit 8 cancels each other out. The impedance shaping coefficient α in the high-pass impedance shaping circuit 1-10 (the ratio of the impedance of the negative feedback branch of the operational amplifier OPA to the impedance of the positive feedback branch of the operational amplifier OPA) can change the EMI current flowing out of the operational amplifier OPA, thereby realizing the shaping of the impedance of the impedance cancellation circuit 9. Let the impedance of the impedance cancellation circuit 9 be equal to that of the injection circuit 8 when it is greater than the resonant frequency and be zero when it is less than the resonant frequency. The band-pass impedance module 1-5 consists of an injection circuit 8, an impedance cancellation circuit 9, and a band-pass impedance shaping circuit 1-11. The impedance cancellation mechanism of its impedance cancellation circuit 9 and the injection circuit 8 is the same. The difference is that the impedance shaping coefficient α in the band-pass impedance shaping circuit 1-11 makes the impedance of the impedance cancellation circuit 9 equal to that of the injection circuit 8 when it is between two resonant frequency ranges and be zero when it is outside the two resonant frequency ranges. Because the band-pass impedance module 1-5 is in parallel with the high-pass impedance module 1-4, the band-pass impedance module 1-5 is used to help the high-pass impedance module 1-4 reduce the impedance within the filtering frequency band that does not meet the set frequency band. The high-pass impedance module 2-6 consists of an injection circuit 8, an impedance cancellation circuit 9, and a high-pass impedance shaping circuit 2-12, and its working mechanism is the same as that of the high-pass impedance module 1-4. The band-pass impedance module 2-7 consists of an injection circuit 8, an impedance cancellation circuit 9, and a band-pass impedance shaping circuit 2-13, and its working mechanism is the same as that of the band-pass impedance module 1-5.

[0091] When suppressing the common-mode electromagnetic interference of the switched-mode power converter 2, the power grid / power supply 1 is equivalent to the impedance Z between the L line and the PE line L and the impedance Z between the N line and the PE line N . The switched-mode power converter 2 is equivalent to a series circuit composed of two identical common-mode voltage sources U CM and a common-mode impedance Z CM . One series circuit is connected in parallel between the L line and the PE line, and the other series circuit is connected in parallel between the N line and the PE line. The impedance of the parallel low-impedance branch 1 composed of the high-pass impedance module 1-4 and the band-pass impedance module 1-5 is less than the load impedance Z L , and the common-mode electromagnetic interference between the L line and the PE line can be filtered out. The impedance of the parallel low-impedance branch 2 composed of the high-pass impedance module 2-6 and the band-pass impedance module 2-7 is less than the load impedance Z N, the common-mode electromagnetic interference of the N line and the PE line can be filtered out.

[0092] When suppressing the differential-mode electromagnetic interference of the switching power converter 2, the power grid / power supply 1 is equivalent to the impedance Z between the L line and the PE line L and the impedance Z between the N line and the PE N sum. The switching power converter 2 is equivalent to a differential-mode voltage source U DM and a differential-mode impedance Z DM series circuit, which is connected in parallel between the L line and the N line. The parallel low-impedance branch one composed of the high-pass impedance module one 4 and the band-pass impedance module one 5 is connected in series with the parallel low-impedance branch two composed of the high-pass impedance module two 6 and the band-pass impedance module two 7, and the impedance of the obtained series low-impedance path is less than the load impedance Z L and Z N sum, and the differential-mode electromagnetic interference of the L line and the N line can be filtered out.

[0093] Embodiment 7

[0094] The design method of the EMI filter with active impedance shaping for common-differential mode simultaneous suppression of the present invention is as follows:

[0095] (1) Design of the injection circuit 8:

[0096] The injection circuit 8 is a high-pass filter composed of an injection resistor R in and an injection capacitor C in connected in series. First, the design of the injection resistor R in is carried out.

[0097] When the frequency exceeds the starting frequency of 150 kHz of the conducted electromagnetic interference, according to the impedance characteristic of the capacitor, the impedance of the injection capacitor C in tends to zero, equivalent to a short circuit, and only the injection resistor R in exists in the injection circuit 8. At this time, according to Ohm's law, the resistance value of the injection resistor R in is:

[0098]

[0099] Among them, U EMI1 is the fundamental harmonic voltage of the switching frequency of the switching power converter; U EMI3 is the third harmonic voltage of the switching frequency of the switching power converter; U EMI5 is the fifth harmonic voltage of the switching frequency of the switching power converter; I OPA is the maximum input current of the operational amplifier.

[0100] According to Joule's law, the rated power P in selected for the injection resistor R Rin is:

[0101]

[0102] Among them, U EMI1 is the fundamental harmonic voltage of the switching frequency of the switching power converter; U EMI3 is the third harmonic voltage of the switching frequency of the switching power converter; U EMI5 is the fifth harmonic voltage of the switching frequency of the switching power converter; R in is the resistance value of the injection resistor.

[0103] The cut-off frequency f0 of the high-pass filter composed of the injection resistor R in and the injection capacitor C in connected in series can be designed according to the impedance shaping frequency f s of the active impedance shaping EMI filter, and its formula is:

[0104]

[0105] Among them, R in is the injection resistor; C in is the injection capacitor; f s is the impedance shaping frequency, generally taking the starting frequency 150 kHz of conducted EMI.

[0106] According to formula (1) and formula (3), the capacitance value of the injection capacitor C in is:

[0107]

[0108] Among them, I OPA is the maximum input current of the operational amplifier; f s is the impedance shaping frequency, generally taking the starting frequency 150 kHz of conducted EMI; U EMI1 is the fundamental harmonic voltage of the switching frequency of the switching power converter; U EMI3 is the third harmonic voltage of the switching frequency of the switching power converter; U EMI5 is the fifth harmonic voltage of the switching frequency of the switching power converter.

[0109] In order to protect the injection capacitor C in , prevent it from being broken down by high voltage, a certain margin needs to be set, that is, the rated voltage U in of the injection capacitor C Cin is:

[0110] U Cin = 1.5U IN (5)

[0111] Among them, U IN is the voltage on the input side of the switching power converter.

[0112] (2) Design of the impedance cancellation circuit 9:

[0113] The impedance cancellation circuit 9 is a high-pass filter composed of a cancellation resistor R io and a cancellation capacitor C io connected in series. Its main function is to generate a negative impedance with an amplitude equal to that of the injection circuit impedance in the electromagnetic interference frequency band, so that the impedance of the entire EMI filter is approximately zero in the electromagnetic interference frequency band. At this time, the impedance Z AEF of the EMI filter has the following formula:

[0114]

[0115] where f s is the impedance shaping frequency, generally taking the starting frequency 150 kHz of conducted EMI; R in is the injection resistor; C in is the injection capacitor; R io is the cancellation resistor; C io is the cancellation capacitor; α is the impedance shaping coefficient, generally taking 0.95.

[0116] In order to make the sum of the impedances of the impedance cancellation circuit 9 and the injection circuit 8 close to zero, the cut-off frequency of the impedance cancellation circuit 9 should be the same as that of the injection circuit 8. The formula for its cut-off frequency is:

[0117]

[0118] where R io is the cancellation resistor; C io is the cancellation capacitor.

[0119] According to formula (6) and formula (7), the formula for the cancellation capacitor C io can be obtained as:

[0120]

[0121] where α is the impedance shaping coefficient, generally taking 0.95; R in is the injection resistor; Z AEF is the impedance that the EMI filter needs to achieve; f s is the impedance shaping frequency, generally taking the starting frequency 150 kHz of conducted EMI; f0 is the cut-off frequency of the impedance cancellation circuit.

[0122] Similarly, according to formula (6) and formula (7), the formula for the cancellation resistor R io can be obtained as:

[0123]

[0124] Among them, α is the impedance shaping coefficient, generally taken as 0.95; R in is the injection resistance; Z AEF is the impedance that the EMI filter needs to achieve; f s is the impedance shaping frequency, generally taken as the starting frequency of conducted EMI, 150 kHz; f0 is the cut-off frequency of the impedance cancellation circuit.

[0125] (3) Design of the high-pass impedance shaping circuit 10:

[0126] The high-pass impedance shaping circuit 10 includes two high-pass shaping resistors R1, a high-pass shaping capacitor C2, and an operational amplifier OPA. Among them, the operational amplifier OPA selects OPA659 of TI Company.

[0127] The impedance Z of the EMI filter AEF is modulated by the ratio of the impedance Z1 of the positive feedback branch and the impedance Z2 of the negative feedback branch of the operational amplifier OPA, and this ratio is defined as the impedance shaping coefficient α. Considering the influence brought by the parasitic parameters of the high-pass shaping capacitor C2 at high frequencies, the parasitic parameters of the high-pass shaping capacitor C2 will cause the impedance shaping coefficient α to decay at high frequencies, so that the impedance of the EMI filter cannot be maintained at a low impedance. Therefore, considering the parasitic resistance R ESR and parasitic inductance L ESL of the high-pass shaping capacitor C2, the formula for the impedance shaping coefficient α is:

[0128]

[0129] Among them, R1 is the high-pass shaping resistor; C2 is the high-pass shaping capacitor; f s is the impedance shaping frequency, generally taken as the starting frequency of conducted EMI, 150 kHz; L ESL is the parasitic inductance of the high-pass shaping capacitor C2; R ESR is the parasitic resistance of the high-pass shaping capacitor C2.

[0130] For the high-pass impedance shaping circuit, its high-pass impedance shaping frequency f s is:

[0131]

[0132] Among them, α is the impedance shaping coefficient; R1 is the high-pass shaping resistor; C2 is the high-pass shaping capacitor.

[0133] According to formula (10) and formula (11), the design formula for the high-pass shaping resistor R1 can be obtained as:

[0134]

[0135] Among them, α is the impedance shaping coefficient, generally taken as 0.95; f s is the impedance shaping frequency, generally taken as the starting frequency 150 kHz of conducted EMI; L ESL is the parasitic inductance of the high-pass shaping capacitor C2; R ESR is the parasitic resistance of the high-pass shaping capacitor C2.

[0136] Similarly, according to formula (10) and formula (11), the design formula for the high-pass shaping capacitor C2 can be obtained as:

[0137]

[0138] Among them, α is the impedance shaping coefficient, generally taken as 0.95; f s is the impedance shaping frequency, generally taken as the starting frequency 150 kHz of conducted EMI; L ESL is the parasitic inductance of the high-pass shaping capacitor C2; R ESR is the parasitic resistance of the high-pass shaping capacitor C2.

[0139] (4) Design of the band-pass impedance shaping circuit 11:

[0140] The band-pass impedance shaping circuit 11 includes two band-pass shaping resistors R3, a band-pass shaping capacitor C3, a band-pass shaping inductor L3, and an operational amplifier OPA. Among them, the operational amplifier OPA selects OPA659 of TI Company.

[0141] The band-pass impedance shaping circuit 11 contains a band-pass shaping capacitor C3 and a band-pass shaping inductor L3. Therefore, according to the frequency characteristics of the LC filter, the center frequency f c of the band-pass impedance shaping circuit 11 has the formula:

[0142]

[0143] Among them, L3 is the band-pass shaping inductor; C3 is the band-pass shaping capacitor.

[0144] According to the design principle of the band-pass filtering frequency band of conducted EMI, another calculation formula for the center frequency f c of the band-pass impedance shaping circuit 1 is:

[0145]

[0146] Among them, f low is the lower limit frequency of the filtering frequency band; BW is the conducted EMI filtering frequency band; f up is the upper limit frequency of the filtering frequency band.

[0147] Based on the impedance shaping principle of the EMI filter, the calculation formula for the impedance shaping coefficient α of the band-pass impedance shaping circuit 11 is:

[0148]

[0149] Among them, R3 is a band-pass shaping resistor; C3 is a band-pass shaping capacitor; L3 is a band-pass shaping inductor; f c is the center frequency of the filtering frequency band.

[0150] In order to ensure that the impedance shaping coefficient α of the band-pass impedance shaping circuit 1 is maintained between 0 and 1, the relationship between the band-pass shaping resistor R3, the band-pass shaping capacitor C3, and the band-pass shaping inductor L3 is:

[0151]

[0152] Among them, k is the multiple of the inductance resistance value at the center frequency of the filtering frequency band. The smaller k is, the better the filtering effect, and the minimum is not less than 0.1; C3 is the band-pass shaping capacitor; L3 is the band-pass shaping inductor.

[0153] According to formulas (14) to (17), the design formula for the band-pass shaping capacitor C3 can be obtained as:

[0154]

[0155] Among them, f c is the center frequency of the filtering frequency band; k is the multiple of the inductance or capacitance resistance value at the center frequency of the filtering frequency band; α is the impedance shaping coefficient, generally taking 0.95.

[0156] Similarly, according to formulas (14) to (17), the design formula for the band-pass shaping inductor L3 can be obtained:

[0157]

[0158] Among them, f c is the center frequency of the filtering frequency band; k is the multiple of the inductance or capacitance resistance value at the center frequency of the filtering frequency band; α is the impedance shaping coefficient, generally taking 0.95.

[0159] Similarly, the design formula for the band-pass shaping resistor R3 is obtained:

[0160]

[0161] Among them, k is the multiple of the inductance or capacitance resistance value at the center frequency of the filtering frequency band; α is the impedance shaping coefficient, generally taking 0.95.

[0162] (5) Design of the high-pass impedance shaping circuit 2 12:

[0163] It is consistent with the design rule of the high-pass impedance shaping circuit 1 10, that is, the high-pass shaping resistor R5 is equal to the high-pass shaping resistor R1, and the high-pass shaping capacitor C6 is equal to the high-pass shaping capacitor C2.

[0164] (6) Design of the band-pass impedance shaping circuit two 13:

[0165] It is consistent with the design rule of the band-pass impedance shaping circuit one 11, that is, the band-pass shaping resistor R8 is equal to the band-pass shaping resistor R3, the band-pass shaping capacitor C8 is equal to the band-pass shaping capacitor C3, and the band-pass shaping inductor L8 is equal to the band-pass shaping inductor L3.

[0166] The measurement waveform diagram of the common-mode conducted EMI suppression of the switching power converter of the active impedance shaping EMI filter with common-difference mode simultaneous suppression of the present invention is as Figure 3 shown, including the blue common-mode interference curve without the filter and the red common-mode interference curve with the active impedance shaping EMI filter. The switching power converter 2 selects the AC / DC switching power supply of Mean Well, and the switching frequency is 90 kHz. The EMI receiver ESL of Rohde & Schwarz is used to measure the common-mode electromagnetic interference on the input side of the Mean Well AC / DC switching power supply. It can be seen from the waveform that after using the active impedance shaping EMI filter, all the electromagnetic interference frequency points meet the national standards, and its insertion loss can reach up to 40 dB.

[0167] The measurement waveform diagram of the differential-mode conducted EMI suppression of the switching power converter of the active impedance shaping EMI filter with common-difference mode simultaneous suppression of the present invention is as Figure 4 shown, including the blue common-mode interference curve without the filter and the red common-mode interference curve with the active impedance shaping EMI filter. The switching power converter 2 selects the AC / DC switching power supply of Mean Well, and the switching frequency is 90 kHz. The EMI receiver ESL of Rohde & Schwarz is used to measure the differential-mode electromagnetic interference on the input side of the Mean Well AC / DC switching power supply. It can be seen from the waveform that after using the active impedance shaping EMI filter, all the electromagnetic interference frequency points meet the national standards, and its insertion loss can reach up to 30 dB.

[0168] The actual impedance measurement waveform diagram of the active impedance shaping EMI filter with common-difference mode simultaneous suppression of the present invention is as Figure 5 shown, including the capacitance output impedance curve of the blue solid line and the output impedance curve of the impedance shaping filter of the red dashed line. The vector network analyzer ZNL of Rohde & Schwarz is used to measure the impedance of the EMC capacitor originally used by the Mean Well AC / DC switching power supply and the output impedance of the active impedance shaping EMI filter. It can be seen from the waveform that the output impedance of the impedance shaping filter is smaller than that of the capacitor, and at 150 kHz, the impedance of the impedance shaping filter reaches 0.113 Ω, realizing low impedance shaping.

[0169] The EMI filter with active impedance shaping for common-mode and differential-mode simultaneous suppression of the present invention can suppress both the common mode and differential mode of a switched-mode power converter, and can quickly achieve ultra-low impedance adjustment according to the electromagnetic interference frequency band to meet the requirements of high power density of the switched-mode power converter. The present invention solves the problems that the current capacitors cannot achieve the equivalent impedance required for filtering in the electromagnetic interference frequency band, resulting in insufficient filtering ability, and the problem that the power density index of the current switched-mode power converter equipped with a passive EMI filter does not meet the standard.

Claims

1. An active impedance shaping EMI filter with simultaneous common and differential mode suppression, characterized in that: It includes a high-pass impedance module (4), wherein the high-pass impedance module (4) and the band-pass impedance module (5) are connected in parallel to form a low-impedance branch (1), and the low-impedance branch (1) is connected in parallel between the L line and the PE line; It also includes a high-pass impedance module 2 (6). The high-pass impedance module 2 (6) and the band-pass impedance module 2 (7) are connected in parallel to form a low-impedance branch 2. The low-impedance branch 2 is connected in parallel between the N line and the PE line.

2. The EMI filter with active impedance shaping and simultaneous common and differential mode suppression according to claim 1, characterized in that: The high-pass impedance module 2 (6) has the same structure as the high-pass impedance module 1 (4). The high-pass impedance module 1 (4) includes a high-pass impedance shaping circuit 1 (10). The high-pass impedance shaping circuit 1 (10) is respectively connected to the injection circuit (8) and the impedance compensation circuit (9).

3. The EMI filter with active impedance shaping and simultaneous common and differential mode suppression according to claim 2, characterized in that: The bandpass impedance module 2 (7) has the same structure as the bandpass impedance module 1 (5). The bandpass impedance module 1 (5) includes a bandpass impedance shaping circuit 1 (11). The bandpass impedance shaping circuit 1 (11) is respectively connected to the injection circuit (8) and the impedance cancellation circuit (9).

4. The EMI filter with active impedance shaping and simultaneous common and differential mode suppression according to claim 3, characterized in that: The injection circuit (8) comprises an injection resistor R in , injection resistor R in and the injection capacitor C in Form a high pass filter.

5. The EMI filter with active impedance shaping and simultaneous common and differential mode suppression according to claim 4, characterized in that: The impedance cancellation circuit (9) comprises a cancellation resistor R io , offset resistance R io and the offset capacitor C io Form a high pass filter.

6. The EMI filter with active impedance shaping and simultaneous common and differential mode suppression according to claim 5, characterized in that: The high-pass impedance shaping circuit 1 (10) comprises an operational amplifier OPA, wherein the positive feedback branch of the operational amplifier OPA is connected in sequence to a high-pass shaping resistor R1 and a high-pass shaping capacitor C2, and the positive feedback branch of the operational amplifier OPA is also connected to a compensation resistor R io The negative feedback branch of the operational amplifier OPA is connected to another high-pass shaping resistor R1 and the injection resistor R in .

7. The EMI filter with active impedance shaping and simultaneous common and differential mode suppression according to claim 6, characterized in that: The passband impedance shaping circuit 1 (11) comprises an operational amplifier OPA, wherein the positive feedback branch of the operational amplifier OPA is respectively connected to a passband shaping resistor R3 and an offset resistor R io , the negative feedback branch of the operational amplifier OPA is connected to another bandpass shaping capacitor C3 and the injection resistor R in , the passband shaping capacitor C3 is connected in parallel with the passband shaping inductor L3 and another passband shaping resistor R3 respectively.

8. The design method of the EMI filter with active impedance shaping for simultaneous common and differential mode suppression according to any one of claims 1 to 7, characterized in that: The design requirements of the injection circuit (8) are as follows: When the frequency exceeds the 150kHz starting frequency of the conducted electromagnetic interference, according to the capacitance impedance characteristics, the impedance of the injection circuit (8) is only equal to the injection resistor R in Regarding the injection capacitor C in The impedance is negligible. According to Ohm's law, the injection resistance R is obtained. in The resistance value is: Among them, U EMI1 is the fundamental harmonic voltage of the switching frequency of the switching power converter; U EMI3 is the third harmonic voltage of the switching frequency of the switching power converter; U EMI5 is the fifth harmonic voltage of the switching frequency of the switching power converter; I OPA is the maximum input current of the operational amplifier; According to Joule's law, the injection resistor R in Selected rated power P Rin for: Injection resistor R in and the injection capacitor C in The cut-off frequency f0 of the high-pass filter composed in series is based on the impedance shaping frequency f of the active impedance shaping EMI filter. s Design, the formula is: According to formula (1) and formula (3), the injection capacitance C is in The value of is: Among them, I OPA is the maximum input current of the operational amplifier OPA; Injection capacitor C in Rated voltage U Cin for: The Cin =1.5U IN (5) Among them, U IN is the input side voltage of the switching power converter.

9. The design method of the EMI filter with active impedance shaping and common and differential mode simultaneous suppression according to claim 8, characterized in that: The design requirements of the impedance cancellation circuit (9) are as follows: The impedance cancellation circuit (9) is a cancellation resistor R io and the offset capacitor C io The high-pass filter formed in series generates a negative impedance equal to the impedance amplitude of the injection circuit in the electromagnetic interference frequency band, making the impedance of the entire EMI filter zero in the electromagnetic interference frequency band. At this time, the impedance of the EMI filter is Z AEF The formula is: Where, α is the impedance shaping coefficient; In order to make the sum of the impedances of the impedance cancellation circuit (9) and the injection circuit (8) equal to zero, the cutoff frequency of the impedance cancellation circuit (9) should be consistent with the cutoff frequency of the injection circuit (8). The formula of the cutoff frequency f0 is: According to formula (6) and formula (7), the offset capacitance C is obtained io The formula is: According to formula (6) and formula (7), the offset resistance R is obtained io The formula is:

10. The design method of the EMI filter with active impedance shaping and common and differential mode simultaneous suppression according to claim 9, characterized in that: The design requirements of the high-pass impedance shaping circuit 1 (10) are as follows: Considering the parasitic resistance R of the high-pass shaping capacitor C2 ESR and parasitic inductance L ESL In the case of, the impedance shaping coefficient α formula is: Among them, R1 is the high-pass shaping resistor; C2 is the high-pass shaping capacitor; L ESL is the parasitic inductance of the high-pass shaping capacitor C2; R ESR is the parasitic resistance of the high-pass shaping capacitor C2; For a high-pass impedance shaping circuit, the high-pass impedance shaping frequency f s for: According to formula (10) and formula (11), the formula of high-pass shaping resistor R1 is: According to formula (10) and formula (11), the formula of high-pass shaping capacitor C2 is: The design requirements of the bandpass impedance shaping circuit 1 (11) are as follows: The bandpass impedance shaping circuit 1 (11) includes a bandpass shaping capacitor C3 and a bandpass shaping inductor L3. Therefore, according to the frequency characteristics of the LC filter, the center frequency f of the bandpass impedance shaping circuit 1 (11) is c The formula is: Among them, L3 is a bandpass shaping inductor; C3 is a bandpass shaping capacitor; According to the design principle of the conducted EMI bandpass filter frequency band, the center frequency f of the bandpass impedance shaping circuit is c Another calculation formula is: Among them, f low is the lower limit frequency of the filter frequency band; BW is the conducted EMI filter frequency band; f up is the upper limit frequency of the filter band; Based on the impedance shaping principle of the EMI filter, the calculation formula of the impedance shaping coefficient α of the bandpass impedance shaping circuit (11) is: Among them, R3 is the bandpass shaping resistor; In order to ensure that the impedance shaping coefficient α of the bandpass impedance shaping circuit 1 is maintained between 0 and 1, the relationship between the bandpass shaping resistor R3, the bandpass shaping capacitor C3 and the bandpass shaping inductor L3 is: Where k is the multiple of the inductor resistance at the center frequency of the filter band; According to formula (14) to formula (17), the design formula of the passband shaping capacitor C3 is: According to formula (14) to formula (17), the design formula of the passband shaping inductor L3 is obtained: According to formula (14) to formula (17), the design formula of the passband shaping resistor R3 is obtained:

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