CN112803755A - Isolated fixed-frequency common-mode resonance suppression method for DC-DC converter - Google Patents

Isolated fixed-frequency common-mode resonance suppression method for DC-DC converter Download PDF

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CN112803755A
CN112803755A CN202011561530.5A CN202011561530A CN112803755A CN 112803755 A CN112803755 A CN 112803755A CN 202011561530 A CN202011561530 A CN 202011561530A CN 112803755 A CN112803755 A CN 112803755A
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common mode
frequency
converter
mode resonance
formula
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苏建徽
金陵
赖纪东
尹浩
马昆
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Hefei University of Technology
State Grid Hubei Electric Power Co Ltd
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Hefei University of Technology
State Grid Hubei Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop

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  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a common mode resonance suppression method for isolated fixed frequency of a DC-DC converter, which comprises the following steps: 1. measuring the impedance of a common mode loop of the DC-DC converter, determining the number and frequency of common mode resonance points existing in the converter, and calculating the value of the required damping resistance; 2. a common mode resonance suppression circuit is connected in series in a main power loop of the DC-DC converter, a primary winding of a transformer of the DC-DC converter is a common mode inductor, and a secondary winding is connected with an attenuator formed by a frequency selection network and a damping resistor in parallel connection; 3. and selecting different frequency selection network structures according to the number of different common mode resonance points so as to inhibit the common mode noise in the specific common mode resonance point of the DC-DC converter and the frequency range nearby the specific common mode resonance point. The invention can flexibly change the circuit structure of the frequency selection network in the common mode resonance suppression circuit aiming at different converter topologies so as to adapt to the influence of the change of the common mode resonance points of different topologies on the bandwidth requirement of the frequency selection network, thereby achieving the effect of suppressing the common mode resonance at a fixed frequency.

Description

Isolated fixed-frequency common-mode resonance suppression method for DC-DC converter
Technical Field
The invention relates to an isolated fixed-frequency common-mode resonance suppression method for a DC-DC converter, which can be applied to DC-DC converters with any topology.
Background
When the DC-DC converter works normally, high-frequency voltage jump is generated at a circuit node, parasitic capacitance of the converter to the ground is excited to generate displacement current, high-frequency common-mode noise current which is formed on two power lines in the same direction and returns on the ground line is formed, when the high-frequency common-mode noise current is large enough, the high-frequency common-mode noise current can interfere electronic equipment at any position in space through radiation, and therefore common-mode interference is formed. With the gradual application of the third generation semiconductor devices, the operating frequency of the DC-DC converter is higher and higher, and the problem of the generated common mode interference is also more and more serious. Especially in a great deal of fields such as distributed photovoltaic power generation access medium-high voltage direct current distribution network, electric automobile direct current fill electric pile, power electronic transformer, the common mode interference problem is especially outstanding. To deal with this problem, electromagnetic interference (EMI) filters are often used in engineering to suppress common mode interference. When the common-mode conducted EMI of the converter is actually measured, one end of the EMI filter is connected with the power converter, namely a noise source, and the other end of the EMI filter is connected with the EMI measuring device, namely a linear impedance stabilization network (LISN, a device for measuring noise current), namely a load, as shown in FIG. 1. In order to achieve the maximum suppression effect, the EMI filter is designed using the impedance mismatch principle, so that the insertion loss of the filter is maximized: if the impedance of the noise source is high impedance, a low impedance element is selected at one end of the EMI filter close to the noise source; if the load is low impedance, the EMI filter selects a high impedance element near the load side. However, for the DC-DC converter, the common mode conductive EMI loop includes both parasitic inductance and parasitic capacitance, and resonance occurs at high frequency, which causes a great reduction in the common mode loop impedance, i.e. it is considered that the noise source impedance is no longer high impedance at this point. At the moment, the EMI filter is no longer in the working condition of impedance mismatch, the insertion loss is greatly reduced, and the common-mode noise of the converter is easy to exceed the regulation limit value at the common-mode resonance point.
To solve this problem, the current solutions mainly include: 1) a resistor is connected in series in the main power loop to achieve the aim of damping and vibration elimination; 2) the EMI filter is redesigned.
However, the above method has the following disadvantages: 1) because the resistor is directly connected in series in the main power loop, larger loss can be brought, and the efficiency of the converter is influenced; 2) the series resistor not only inhibits useless high-frequency common mode current, but also has an inhibiting effect on fundamental frequency or low-frequency differential mode current required by the normal operation of the converter, and the normal operation of the converter can be influenced; 3) redesigning the filter requires a larger insertion loss margin, increasing filter size and cost.
Disclosure of Invention
The invention aims to avoid the defects of the prior art and provides an isolated fixed-frequency common-mode resonance suppression method for a DC-DC converter, aiming at different converter topologies, the circuit structure and the element parameters of a frequency selection network in a common-mode resonance suppression circuit can be flexibly changed, so as to adapt to the influence of the change of common-mode resonance points of different topologies on the bandwidth requirement of the frequency selection network, and further achieve the effect of fixed-frequency common-mode resonance suppression.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the invention discloses a common mode resonance suppression method of isolated fixed frequency of a DC-DC converter, which is characterized by comprising the following steps:
step 1: measuring the common-mode loop impedance of the DC-DC converter, and determining the number n and the frequency f of common-mode resonance points of the DC-DC converter1、f2、…、fnAnd calculating the required damping resistance RcmThe resistance value of (1); f. ofnRepresenting the frequency of the nth common mode resonance point;
step 2: a common mode resonance suppression circuit is connected in series in a main power loop of the DC-DC converter and is formed by transforming a common mode voltageThe primary winding of the common mode transformer is a common mode inductor LcmThe secondary winding is connected with the attenuator which is formed by connecting a frequency-selecting network with an upper damping resistor R in parallelcmAnd then the product is obtained;
and step 3: selecting different frequency selection network structures according to the number n of common mode resonance points to inhibit the DC-DC converter from being at the n common mode resonance points and the frequency f thereof1、f2、…、fnCommon mode noise in the vicinity.
The invention also discloses a common mode resonance suppression method of the isolated fixed frequency of the DC-DC converter, which is characterized in that the damping resistor RcmIs calculated by calculating the characteristic impedance Z of the DC-DC converter1、Z2、……ZnAnd taking the maximum value to obtain:
step 2.1: calculation of characteristic impedance Z of DC-DC converter by using equation (1)1、Z2、……Zn：
Figure BDA0002860574280000021
In the formula (1), L1、L2、…、Ln、C1、C2、…、CnEquivalent parasitic inductance and equivalent parasitic capacitance of a common mode loop of the DC-DC converter; l isnRepresenting the nth common mode resonance point frequency fnEquivalent parasitic inductance in the vicinity; cnRepresenting the nth common mode resonance point frequency fnEquivalent parasitic capacitance in the vicinity
Step 2.2: obtaining the damping resistance R by using the formula (2)cmResistance value of (2):
Rcm＝max{Z1,Z2,…,Zn} (2)。
the invention also discloses a common mode resonance suppression method of the isolated fixed frequency of the DC-DC converter, which is characterized in that the frequency selection network consists of an inductance capacitor, one end of the frequency selection network is connected with a secondary winding of the common mode transformer, and the other end of the frequency selection network is connected with a damping resistor RcmThe structure of the frequency-selective networkFrom the number n of common mode resonance points and the frequency f thereof1、f2、…、fnDetermining:
when the number n of the common mode resonance points is 1, the frequency selection network has a structure of a single filter capacitor CcmAnd is connected with a common mode inductor LcmDamping resistor RcmThe common mode inductor L is obtained by using a formula (3) and a formula (4) respectivelycmFilter capacitor CcmThe value of (A) is as follows:
Figure BDA0002860574280000022
Figure BDA0002860574280000031
in the formula (3), fm1Represents the turning frequency and has:
Figure BDA0002860574280000032
when the number n of the common mode resonance points is 2, the structure of the frequency selection network is the filter capacitor C in the frequency selection network when the number n of the common mode resonance points is 1cmAnd a damping resistor RcmA secondary filter inductor L is added betweencm1And a filter capacitor Ccm1A branch formed by connecting in series;
obtaining common mode inductance L by using formula (3) and formula (5)cmA value of (d);
obtaining the transition frequency f by the formula (6)m2：
Figure BDA0002860574280000033
Obtaining the common mode inductance L by the formula (7)cmFilter capacitor CcmBranch impedance Z after parallel connectionm：
Figure BDA0002860574280000034
The filter inductance L is obtained by the formula (8)cm1And a filter capacitor Ccm1Branch impedance Z after series connectionm1：
Figure BDA0002860574280000035
Will resonate at a frequency f1、f2Substituted for formula (9) of converting the frequency fm2Substituting formula (10) to obtain filter inductor Lcm1Filter capacitor CcmAnd Ccm1The value of (A) is as follows:
Zm＝Zm1 (9)
Figure BDA0002860574280000036
when the number n of the common mode resonance points is more than or equal to 3, the frequency selection network is set to be an open circuit, so that the secondary winding of the common mode transformer in the common mode rejection circuit is only connected with a damping resistor RcmThereby obtaining a common mode inductance L by using the formula (3) and the formula (5)cmThe value of (c).
Compared with the prior art, the invention has the beneficial effects that:
1. the common mode resonance suppression method has universality, can be suitable for any DC-DC converter topology, can suppress the noise of the common mode resonance point of the DC-DC converter at a fixed frequency without introducing extra loss, cannot influence the normal operation of the DC-DC converter, does not need to redesign a filter with larger insertion loss allowance, and saves the volume and the cost of the DC-DC converter.
2. The invention is based on a damping resistor RcmThe idea of decoupling from the main power loop of the DC-DC converter is that the common-mode transformer is connected in series in the main power loop of the DC-DC converter, so that only useless common-mode current of the DC-DC converter can flow through the damping resistor R connected on the secondary winding of the common-mode transformercmRealize the damping resistance RcmThe isolation and the decoupling with the main power loop of the DC-DC converter overcome the defect that the damping resistor R is directly connected with the damping resistor R in the prior artcmThe large loss caused by the series connection of the main power loop of the DC-DC converter and the adverse effect on the normal operation of the DC-DC converter.
3. According to the invention, different frequency selection network structures are selected according to the number n of common mode resonance points, so that the influence of the change of topology common mode resonance points of different DC-DC converters on the bandwidth requirement of the frequency selection network is adapted, and the method has universality.
4. Based on the idea of suppressing the noise of the common mode resonance point of the DC-DC converter at the fixed frequency, the secondary winding of the common mode transformer is connected with a frequency selection network and a damping resistor RcmThe combined attenuator overcomes the adverse effect of redesigning an EMI filter on the volume and the cost of the DC-DC converter in the prior art, and inhibits the noise of a common mode resonance point of the DC-DC converter at a fixed frequency, so that the DC-DC converter can meet the requirement of the regulation limit value by using the original EMI filter.
Drawings
FIG. 1 is a schematic diagram of a DC-DC converter common mode conducted EMI measurement arrangement;
FIG. 2 is a schematic diagram of the impedance of the common mode loop of the DC-DC converter;
FIG. 3 is a schematic diagram of a DC-DC converter with a full bridge LLC topology;
FIG. 4 is a schematic diagram of an impedance curve of a common mode loop of a DC-DC converter with a full-bridge LLC topology;
FIG. 5 is a schematic diagram of a DC-DC converter with a full-bridge LLC topology after a common mode resonance suppression circuit is connected;
FIG. 6 is a schematic diagram of a common mode resonance suppression circuit according to the present invention;
FIG. 7 is an equivalent circuit diagram of the present invention;
FIG. 8 is a schematic diagram of an equivalent common mode loop after a DC-DC converter is connected in series with the circuit of the present invention;
FIG. 9 is a schematic diagram of the impedance curve of the common mode loop after the DC-DC converter is connected to the common mode resonance suppression circuit;
Detailed Description
In this embodiment, the topology is a full-bridge LLC DC-DCThe transducer structure is shown in fig. 3, and comprises: input side filter capacitor CholdupInput side switching tube Q1～Q4And its freewheeling diode D1～D4Resonant inductance LrResonant capacitor CrTransformer, output side diode D5～D6And an output side filter capacitor Cout。
A common mode resonance suppression method for isolated fixed frequency of a DC-DC converter comprises the following steps:
step 1: common-mode loop impedance Z of DC-DC converter with full-bridge LLC as topological structure for measurementsDetermining the number n of common mode resonance points and the frequency f of the common mode resonance points existing in the DC-DC converter, as shown in FIG. 21、f2、…、fnAs shown in fig. 4, n is 1 at frequency point f1The common mode resonance point occurs at 2.099MHz, and the common mode loop impedance is at f1And the frequency near the EMI filter is sharply reduced, so that the insertion loss of the EMI filter at the point and the frequency near the point is not enough to cause the standard exceeding of common mode noise. Only 1 common mode resonance point f exists because of the DC-DC converter1The common mode loop impedance Z ofsUsable stray resistance Rs1Equivalent parasitic inductance L of 1.1 Ω111.5uH, equivalent parasitic capacitance C1A series circuit of 0.5nF was fitted.
Step 2: a common mode resonance suppression circuit is connected in series in a main power loop of the DC-DC converter, as shown in figure 5, the common mode resonance suppression circuit is composed of a common mode transformer and an attenuator, as shown in figure 6, a primary side winding of the common mode transformer is a common mode inductor LcmThe secondary winding is connected with an attenuator which is formed by connecting a frequency-selecting network with an upper damping resistor R in parallelcmAnd (4) preparing the composition. In the common mode transformer shown in fig. 6, the magnetic fluxes excited in the transformer by the differential mode currents cancel each other out, and no voltage is induced in the secondary winding. Therefore, the common mode resonance suppression circuit does not have an attenuation effect on the differential mode current, is equivalent to a conducting wire and realizes the damping resistance RcmAnd the isolation and the decoupling with the main power loop do not introduce extra loss and influence the normal operation of the converter. However, the common mode current is in the common mode inductance LcmThe magnetic fluxes excited in the secondary winding are superposed with each other, and a voltage is induced in the secondary winding. At this time, the common mode resonance suppression circuit is equivalent to a circuit network shown in fig. 7, which is composed of a common mode inductor LcmFrequency-selecting network and damping resistor R reduced to primary sidecmAnd (4) forming. Because the common mode resonance suppression circuit only needs to increase the common mode loop impedance of the DC-DC converter at the common mode resonance frequency point and the nearby frequency, the EMI filter can suppress the common mode noise at the common mode resonance point and the nearby frequency by working again under the working condition of impedance mismatch, and therefore, the common mode noise current at the specific frequency point can pass through the damping resistor R through the structure and parameter change of the frequency selection networkcmTherefore, the effect of noise of the common mode resonance point of the constant frequency attenuation converter is achieved.
And step 3: selecting different frequency selection network structures according to the number n of common mode resonance points to inhibit the DC-DC converter from being at the n common mode resonance points and the frequency f thereof1、f2、…、fnCommon mode noise in the vicinity. In the embodiment, n is 1, and the frequency selection network is structured by a single filter capacitor CcmAnd is connected with a common mode inductor LcmDamping resistor RcmAnd forming the RLC parallel band-pass filter. Therefore, as shown in fig. 8, the equivalent common mode loop of the DC-DC converter connected in series with the circuit of the present invention can allow the common mode noise current at the common mode resonance point and the frequency near the common mode resonance point to pass through the damping resistor R by reasonable parameter settingcm。
And 4, step 4: damping resistor RcmIs calculated by calculating the characteristic impedance Z of the DC-DC converter1、Z2、……ZnAnd taking the maximum value, i.e. calculating the characteristic impedance Z of the DC-DC converter using equation (1)1、Z2、……Zn：
Figure BDA0002860574280000051
In the formula (1), L1、L2、…、Ln、C1、C2、…、CnEquivalent parasitic inductance and equivalent parasitic capacitance of a common mode loop of the DC-DC converter; l isnRepresenting the nth common mode resonance point frequency fnEquivalent parasitic inductance in the vicinity; cnRepresenting the nth common mode resonance point frequency fnEquivalent parasitic capacitance in the vicinity; obtaining the damping resistance R by using the formula (2)cmResistance value of (2):
Rcm＝max{Z1,Z2,…,Zn} (2)
since n is 1 in this example, RcmThe value of (a) is obtained by the formula (3):
Figure BDA0002860574280000052
at this time, at the common mode resonance point f1Here, the attenuation coefficient γ of the common mode loop is obtained by equation (4):
Figure BDA0002860574280000061
attenuation coefficient gamma > 1, common mode resonance point f1The common mode noise is suppressed.
And 5: when the number n of common mode resonance points is 1, the structure of the frequency selection network is a single filter capacitor CcmAnd is connected with a common mode inductor LcmDamping resistor RcmThe RLC parallel band-pass filter is formed, the measurement error and the tolerance range of common-mode rejection circuit elements are considered, the frequency selection network has a certain bandwidth, and common-mode noise current mainly flows through R in the bandwidth rangecmAnd the fixed frequency inhibits common mode noise. Thus the turning frequency fm1DC-DC converter common mode loop impedance set when common mode rejection circuit is not connected
Figure BDA0002860574280000068
The frequency point of time, therefore, f is obtained from the formula (5)m1：
Figure BDA0002860574280000062
By using(6) And (7) obtaining the common mode inductance LcmFilter capacitor CcmThe value of (A) is as follows:
Figure BDA0002860574280000063
Figure BDA0002860574280000064
above the transition frequency fm1Then, the common mode noise current mainly flows through the damping resistor RcmImpedance curve Z of common mode loop of DC-DC converter without access to common mode resonance suppression circuitsCommon mode resonance suppression circuit impedance curve ZcmCommon-mode loop impedance curve Z after DC-DC converter is connected into common-mode resonance suppression circuitcm+ZsThe impedance at the common mode resonance point and its vicinity is raised to R as shown in FIG. 9cm+Rs1While the common-mode impedance at other points is not changed, so the damping resistance R is not changedcmAnd only common mode noise in a common mode resonance point and a frequency range nearby the common mode resonance point is restrained, and the common mode noise in other ranges is not influenced.
When the number n of common mode resonance points is 2, the structure of the frequency selection network is the filter capacitor C in the frequency selection network when the number n of common mode resonance points is 1cmAnd a damping resistor RcmA secondary filter inductor L is added betweencm1And a filter capacitor Ccm1A branch formed by connecting in series;
obtaining common mode inductance L by using formula (5) and formula (6)cmA value of (d);
obtaining the transition frequency f by the formula (8)m2：
Figure BDA0002860574280000065
Obtaining the common mode inductance L by the formula (9)cmFilter capacitor CcmBranch impedance Z after parallel connectionm：
Figure BDA0002860574280000066
Filter inductance L obtained by using formula (10)cm1And a filter capacitor Ccm1Branch impedance Z after series connectionm1：
Figure BDA0002860574280000067
Will resonate at a frequency f1、f2Substituted for formula (11), converting the frequency fcm2Substituting formula (12) to obtain filter inductor Lcm1Filter capacitor CcmAnd Ccm1The value of (A) is as follows:
Zm＝Zm1 (11)
Figure BDA0002860574280000071
when the number n of the common mode resonance points is more than or equal to 3, the frequency selection network is set to be an open circuit, so that the secondary winding of the common mode transformer in the common mode rejection circuit is only connected with a damping resistor RcmThereby obtaining a common mode inductance L using the equations (5) and (6)cmThe value of (c).
In summary, the invention designs an isolated type constant frequency and common mode resonance suppression method for a DC-DC converter based on the idea of decoupling a damping resistor from a main power loop and allowing the damping resistor to suppress common mode noise at a constant frequency in a common mode resonance point and in a frequency range near the common mode resonance point, and is suitable for any DC-DC converter topology.

Claims (3)

1. A common mode resonance suppression method of isolated fixed frequency of a DC-DC converter is characterized by comprising the following steps:
step 1: measuring the common-mode loop impedance of the DC-DC converter, and determining the number n and the frequency f of common-mode resonance points of the DC-DC converter1、f2、…、fnAnd calculating the required damping resistance RcmThe resistance value of (1); f. ofnRepresenting the frequency of the nth common mode resonance point;
step 2: a common mode resonance suppression circuit is connected in series in a main power loop of the DC-DC converter, the common mode resonance suppression circuit consists of a common mode transformer and an attenuator, and a primary winding of the common mode transformer is a common mode inductor LcmThe secondary winding is connected with the attenuator which is formed by connecting a frequency-selecting network with an upper damping resistor R in parallelcmAnd then the product is obtained;
and step 3: selecting different frequency selection network structures according to the number n of common mode resonance points to inhibit the DC-DC converter from being at the n common mode resonance points and the frequency f thereof1、f2、…、fnCommon mode noise in the vicinity.
2. The isolated fixed-frequency common-mode resonance suppression method for the DC-DC converter according to claim 1, wherein the damping resistor RcmIs calculated by calculating the characteristic impedance Z of the DC-DC converter1、Z2、……ZnAnd taking the maximum value to obtain:
step 2.1: calculation of characteristic impedance Z of DC-DC converter by using equation (1)1、Z2、……Zn：
Figure FDA0002860574270000011
In the formula (1), L1、L2、…、Ln、C1、C2、…、CnEquivalent parasitic inductance and equivalent parasitic capacitance of a common mode loop of the DC-DC converter; l isnRepresenting the nth common mode resonance point frequency fnEquivalent parasitic inductance in the vicinity; cnRepresenting the nth common mode resonance point frequency fnEquivalent parasitic capacitance in the vicinity;
step 2.2: obtaining the damping resistance R by using the formula (2)cmResistance value of (2):
Rcm＝max{Z1,Z2,···,Zn} (2)。
3. the isolated fixed-frequency common-mode resonance suppression method for the DC-DC converter according to claim 1, wherein the frequency selection network is composed of an inductor capacitor, one end of the frequency selection network is connected to a secondary winding of the common-mode transformer, and the other end of the frequency selection network is connected to a damping resistor RcmThe structure of the frequency-selecting network consists of the number n of common-mode resonance points and the frequency f thereof1、f2、…、fnDetermining:
when the number n of the common mode resonance points is 1, the frequency selection network has a structure of a single filter capacitor CcmAnd is connected with a common mode inductor LcmDamping resistor RcmThe common mode inductor L is obtained by using a formula (3) and a formula (4) respectivelycmFilter capacitor CcmThe value of (A) is as follows:
Figure FDA0002860574270000012
Figure FDA0002860574270000013
in the formula (3), fm1Represents the turning frequency and has:
Figure FDA0002860574270000021
when the number n of the common mode resonance points is 2, the structure of the frequency selection network is the filter capacitor C in the frequency selection network when the number n of the common mode resonance points is 1cmAnd a damping resistor RcmA secondary filter inductor L is added betweencm1And a filter capacitor Ccm1A branch formed by connecting in series;
obtaining common mode inductance L by using formula (3) and formula (5)cmA value of (d);
obtaining the transition frequency f by the formula (6)m2：
Figure FDA0002860574270000022
Obtaining the common mode inductance L by the formula (7)cmFilter capacitor CcmBranch impedance Z after parallel connectionm：
Figure FDA0002860574270000023
The filter inductance L is obtained by the formula (8)cm1And a filter capacitor Ccm1Branch impedance Z after series connectionm1：
Figure FDA0002860574270000024
Will resonate at a frequency f1、f2Substituted for formula (9) of converting the frequency fcm2Substituting formula (10) to obtain filter inductor Lcm1Filter capacitor CcmAnd Ccm1The value of (A) is as follows:
Zm＝Zm1 (9)
Figure FDA0002860574270000025
when the number n of the common mode resonance points is more than or equal to 3, the frequency selection network is set to be an open circuit, so that the secondary winding of the common mode transformer in the common mode rejection circuit is only connected with a damping resistor RcmThereby obtaining a common mode inductance L by using the formula (3) and the formula (5)cmThe value of (c).
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Cited By (1)

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CN114190041A (en) * 2021-11-08 2022-03-15 陕西千山航空电子有限责任公司 Power module electromagnetic interference filtering structure

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Application publication date: 20210514