CN1851973B - Broadband High Attenuation Common Mode Conducted Electromagnetic Interference Parallel Hybrid Filter - Google Patents

Abstract

The invention discloses a wide-band high-attenuation common-mode conduction electromagnetic interference parallel hybrid filter, which includes a passive common-mode filter inductor LCM, the input end of the passive common-mode filter inductor LCM and the output of a high-frequency current transformer LCT The terminals are connected in series to form an active filter and a passive filter; the passive common-mode filter inductor is connected in series with the noise source equipment, which can effectively filter out high-frequency electromagnetic noise and correct the source impedance characteristics of the equipment. The output of the operational amplifier is connected in parallel to the input of a small passive common-mode inductor through two high-voltage ceramic capacitors and resistors, and works in an open-loop state. Its input is connected in series to the power grid side of the equipment through a high-frequency current transformer. The present invention is superior to the simple active or passive filter that constitutes it, and is far greater than the sum of active and passive filtering effects. It has the characteristics of simple and reasonable structure, strong noise attenuation ability, small size and light weight. It can meet the conduction electromagnetic interference suppression of power electronic equipment such as switching power supply.

Description

Broadband High Attenuation Common Mode Conducted Electromagnetic Interference Parallel Hybrid Filter

technical field

The invention belongs to the field of production and application of electromagnetic interference filters, and relates to a parallel hybrid active electromagnetic interference filter with wide frequency band and high attenuation multiple.

Background technique

While power electronic devices are widely used and developed rapidly, the problem of electromagnetic interference (EMI) is becoming more and more serious. Especially in recent years, power converters are constantly moving towards high-frequency, high-efficiency, and high-power-density technologies. This is a huge challenge for how to effectively suppress the electromagnetic noise generated by switching devices. The passive EMI filter composed of passive components such as inductors and capacitors that is widely used at present is bulky in the low frequency band, and the filtering effect is not good, but it shows good filtering performance in the relatively high frequency part. The active filter is limited by the gain-bandwidth product of the active component itself, although it has excellent noise attenuation capability in the low frequency part, it is difficult to obtain a relatively large noise attenuation factor in a wide frequency range, especially in the high frequency band. According to the data retrieval conducted by the applicant, there are no products and related reports of a parallel hybrid common-mode EMI filter composed of active components such as operational amplifiers and passive inductive components.

Contents of the invention

The purpose of the present invention is to provide a wide-band high-attenuation common-mode conducted electromagnetic interference parallel hybrid filter. On the one hand, the hybrid filter overcomes the traditional passive EMI filter. The passive filter has the advantages of good high-frequency filtering effect and small size; on the other hand, it overcomes the shortcomings of the active filter's insufficient high-frequency noise attenuation, and retains the active filter's low-frequency compensation ability and small size. advantage. The hybrid EMI filter realizes the advantages and disadvantages of active and passive filters, and is especially suitable for the conduction electromagnetic interference suppression of power electronic devices such as switching power supplies.

The technical solution to achieve the above purpose is: a wide-band high-attenuation common-mode conducted electromagnetic interference parallel hybrid filter, characterized in that the filter includes a passive common-mode filter inductor L _CM , the passive common-mode filter The input end of the inductor L _CM is connected in series with the output end of the high-frequency current transformer L _CT to form a hybrid filter of an active filter and a passive filter;

The winding directions of the primary and secondary windings of the passive common mode filter inductor L _CM are the same, and the primary and secondary windings are respectively connected in series with the incoming line terminals of the noise source equipment;

The high-frequency current transformer L _CT is respectively wound with 3 windings, and the 3 windings are all wound in the same phase. Two of the windings are connected in series to the output end of the impedance stabilization network LISN, one end of the other winding is grounded, and the other end of the winding is Connect one input terminal of the operational amplifier through a series resistor _R1 , the other input terminal of the operational amplifier is grounded through a resistor _R2 , and the output terminal of the operational amplifier connects the output signal to the passive common mode inductor _LCM through two high-voltage ceramic capacitors The input terminal, the output terminal of the operational amplifier is also grounded through a resistor _R3 .

The filter uses a small passive common-mode inductor, which corrects the impedance characteristics of the noise source equipment and makes its load characteristics more inductive, which is beneficial to the application of parallel active filters. At the same time, the electromagnetic noise in the high frequency band can be easily eliminated. Small inductance filters out. Compared with traditional passive EMI filter components, the inductor has greatly reduced dimensions and weight.

The filtering effect of the filter of the present invention is not only significantly improved and improved compared with a simple passive or active filter. Moreover, the filtering effect of the parallel hybrid EMI filter involved in the present invention is far greater than the sum of the filtering effects of the active and passive filters, and the mixing is not simple addition. The filter has the characteristics of simple circuit structure, convenient design, small size, light weight, strong noise attenuation ability, etc., and is especially suitable for the conduction electromagnetic interference suppression of power electronic devices such as switching power supplies.

Description of drawings

Fig. 1 is the schematic diagram of the circuit structure of the electromagnetic interference active hybrid filter of the present invention;

Fig. 2 is the theoretical model diagram of the electromagnetic interference active hybrid filter of the present invention;

Fig. 3 is the photo that electromagnetic interference active hybrid filter of the present invention is applied to actual device;

Fig. 4 is the experimental result of the electromagnetic interference active hybrid filter of the present invention;

The working principle of the present invention for common-mode electromagnetic interference suppression at the AC input terminal of a 300W computer switching power supply will be further described in detail with reference to the accompanying drawings, the embodiment realized by the inventor.

Detailed ways

With reference to Fig. 1 and Fig. 2, wide-band high-attenuation common-mode conducted electromagnetic interference parallel hybrid filter of the present invention comprises a passive common-mode filter inductor L _CM , the input end of this passive common-mode filter inductor L _CM is connected to the high The output ends of the frequency current transformer L _CT are connected in series to form a hybrid filter of passive filter and active filter;

The winding directions of the primary and secondary windings of the passive common mode filter inductor L _CM are the same, and the primary and secondary windings are respectively connected in phase with the incoming line terminals of the noise source equipment;

The high-frequency current transformer L _CT has three windings respectively, and the three windings are all wound in the same phase. Two of the windings are connected in series to the output end of the impedance stabilization network LISN, and one end of the other winding is grounded, and the other end passes through a resistor R ₁ is connected in series to one input terminal (negative pole) of operational amplifier A, the other input terminal (positive pole) of operational amplifier A is grounded through a resistor R ₂ , and the output terminal of operational amplifier A is connected to the output signal through two high-voltage ceramic capacitors. The input terminal of the passive small common-mode inductor L _CM and the output terminal of the operational amplifier A are grounded through a resistor _R3 .

The source common-mode filter inductor L _CM is made of amorphous material, and the operational amplifier A works in an open-loop state, that is, there is no electrical connection between the input terminal and the output terminal.

Since the signal of the active part of the hybrid filter is connected in parallel to the input terminal of the noise source device, a compensation current equal to and opposite to the noise current is generated and injected into the grid, so it can be equivalent to a controlled current source. Assuming that the open-loop gain of the source part is A, the reactance of the passive common-mode filter inductor is Z ₁ , the common-mode equivalent resistance of the source impedance stabilization network LISN is R, and the equivalent common-mode impedance of the noise source equipment is Z _n , Then the parallel hybrid EMI filter involved in the present invention can be described by the model shown in FIG. 2 .

In this model, when the system only uses passive common-mode filter inductors, the insertion loss (insertionloss---IL) is

${\mathrm{<span\; class="notranslate">\; IL</span>}}_{\mathrm{<span\; class="notranslate">\; passive</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

When the system uses a pure active filter, the insertion loss is

${\mathrm{<span\; class="notranslate">\; IL</span>}}_{\mathrm{<span\; class="notranslate">\; active</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; AZ</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

If the system adopts active and passive hybrid structure, the insertion loss is

${\mathrm{<span\; class="notranslate">\; IL</span>}}_{\mathrm{<span\; class="notranslate">\; hybrid</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; AZ</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; AZ</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

It can be seen that the active and passive hybrid filter structure can obtain higher attenuation than any simple filter, and its noise attenuation capability is much greater than the simple addition of active and passive filter noise attenuation.

The operational amplifier mainly realizes the further amplification of the detection signal. In order to obtain higher gain, the operational amplifier operates in an open-loop state. At the same time, the bandwidth of the operational amplifier should be wide enough, so that the noise signals in the frequency band detected by the transformer can be amplified without distortion. According to the national electromagnetic compatibility design standard, the interference test frequency range of information electronic equipment is 150kHz ~ 30MHz, so the bandwidth of the operational amplifier should not be lower than 50MHz.

The photo of the active hybrid electromagnetic interference filter completed by the inventor according to the above technical scheme applied to a 300W computer switching power supply is shown in Figure 3. The common mode filtering small inductor is made of amorphous material with a diameter of 30mm. The primary and secondary windings are 16 turns in average. The current sampling transformer is a ferrite core with a diameter of 18mm. The resistor R1 is 10kΩ, the balance resistor R2 is 10kΩ, the operational amplifier model is THS4001, and the output capacitor is a high-voltage magnetic chip capacitor, 3300pF/2kV. The test results are shown in Figure 4. Experiments have proved that the design purpose has been achieved.

Claims (5)

1. A wide-band high-attenuation common-mode conducted electromagnetic interference parallel hybrid filter is characterized in that the filter comprises a passive common-mode filter inductor (L _CM ), and the passive common-mode filter inductor (L _CM ) The input end of the high-frequency current transformer (L _CT ) is connected in series with the output end of the high-frequency current transformer (L CT ), forming a hybrid filter of an active filter and a passive filter; The winding directions of the primary and secondary windings of the passive common mode filter inductor (L _CM ) are the same, and the primary and secondary windings are respectively connected in series with the incoming line terminals of the noise source equipment; The high-frequency current transformer (L _CT ) has 3 windings respectively, and the 3 windings are all wound in the same phase. Two of the windings are connected in series to the output end of the impedance stabilization network (LISN), and one end of the other winding is grounded. The other end of the operational amplifier is connected to one input terminal of the operational amplifier through a series resistor (R ₁ ), the other input terminal of the operational amplifier is grounded through a resistor (R ₂ ), and the output terminal of the operational amplifier is connected to the output signal through two high-voltage ceramic capacitors. The input terminal of the passive common mode inductor (L _CM ), the output terminal of the operational amplifier is also grounded through the resistor (R ₃ ). 2. The broadband high-attenuation common-mode conducted electromagnetic interference parallel hybrid filter according to claim 1, characterized in that the passive common-mode filter inductor (L _CM ) is made of amorphous material. 3. wide-band high attenuation common-mode conduction electromagnetic interference parallel hybrid filter as claimed in claim 1, is characterized in that, described operational amplifier works in open-loop state, namely between the input terminal and the output terminal of operational amplifier There are no electrical connections. 4. The wide-band high-attenuation common-mode conducted electromagnetic interference parallel hybrid filter as claimed in claim 1, wherein the values of the two high-voltage ceramic capacitors are on the order of pF. 5. The broadband high-attenuation common-mode conducted electromagnetic interference parallel hybrid filter as claimed in claim 1, wherein the bandwidth of the operational amplifier is not less than 50MHz.

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