CN210867500U - EMI power filter - Google Patents
EMI power filter Download PDFInfo
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- CN210867500U CN210867500U CN201921372542.6U CN201921372542U CN210867500U CN 210867500 U CN210867500 U CN 210867500U CN 201921372542 U CN201921372542 U CN 201921372542U CN 210867500 U CN210867500 U CN 210867500U
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Abstract
The utility model provides an EMI power filter, including the LISN module, the noise separator, equipment under test and receiver, the LISN module is used for providing stable line impedance, keep apart the electric wire netting and disturb, the interference coupling that produces equipment under test is to the receiver on, prevent grid voltage to add on the receiver, the receiver is used for the analysis to correspond the interference voltage size of frequency point, it has equipment under test to connect through the LISN module between the live wire input of electric wire netting and the zero line input of electric wire netting, the LISN module coupling forms live wire interference voltage terminal and zero line interference voltage terminal, the receiver connects in live wire interference voltage terminal and zero line interference voltage terminal, the noise separator sets up between LISN module and receiver, a separation common mode interference and differential mode interference. The utility model discloses can separate common mode interference and differential mode interference, effectively reduce EMI noise.
Description
Technical Field
The utility model relates to an electronic filter technical field, concretely relates to EMI power filter.
Background
Electromagnetic interference (EMI) is generated by the high frequency switching action of the switching power supply during operation, and therefore, the design of electromagnetic compatibility must be considered in designing the switching power supply to meet the requirements of relevant electromagnetic compatibility standards and ensure the normal operation of the consumer electronic equipment. Before entering the market, the power supply product must pass the test certification of conducted interference, and the purpose of adding an EMI filter in the product is to ensure that the power supply product meets the requirements of the corresponding conducted interference standard. Although the existing EMI power filter can meet the requirement of low-frequency characteristics of EMI filtering of a switching power supply, for the actual EMI filter, high-frequency interference formed by parasitic inductance and capacitance in a switching device and a transformer in the switching power supply is considered, so that the design of the filter needs to be corrected for many times in the whole frequency band range meeting the relevant electromagnetic compatibility standard, the filter is often not effective in the frequency range specified by the EMC standard, and EMI noise cannot be effectively reduced.
SUMMERY OF THE UTILITY MODEL
In view of the above, the present invention provides an EMI power filter.
In order to solve the technical problem, the utility model discloses a technical scheme is: an EMI power filter comprises an LISN module, a noise separator, a tested device and a receiver, wherein the LISN module is used for providing stable line impedance, isolating power grid interference, coupling interference generated by the tested device to the receiver and preventing power grid voltage from being added to the receiver, the receiver is used for analyzing interference voltage of corresponding frequency points, a live wire input end of a power grid and a zero line input end of the power grid are connected with the tested device through the LISN module, the LISN module is coupled to form a live wire interference voltage terminal and a zero line interference voltage terminal, the receiver is connected to the live wire interference voltage terminal and the zero line interference voltage terminal, and the noise separator is arranged between the LISN module and the receiver and used for separating common mode interference and differential mode interference.
In the present invention, preferably, the noise separator is configured as a differential mode suppression network, the differential mode suppression network includes two resistors R1 and a resistor R2, two one end of the resistor R1 and the LISN module are connected, two the other end of the resistor R1 is connected in parallel and then connected in series with one end of the resistor R2, the other end of the resistor R2 is connected to the receiver.
The utility model discloses in, preferably, the noise separator sets up to the merit and divides the ware, the merit is divided the ware and is set up to 0 merit and divide the ware with 180 merits, 0 merit is divided the ware and is used for summating live wire interference voltage terminal and zero line interference voltage terminal, obtains the interference to containing common mode signal, 180 merits divide the ware to be used for doing the difference to live wire interference voltage terminal and zero line interference voltage terminal, obtains the interference that only contains the differential mode signal.
In the present invention, it is preferable that the resistance values of two R1 be equal.
In the present invention, it is preferable that the EMI filter further includes a common mode inductor choke coil LCDifferential mode inductance choke LDDifferential mode capacitor CxAnd a common mode capacitor CyThe equivalent simplification is carried out to a common mode equivalent circuit and a differential mode equivalent circuit, namely a common mode inductance choke coil LCHas a leakage inductance of Lleak。
In the present invention, preferably, the common mode equivalent circuit includes a common mode interference source VCMCommon mode source impedance ZCMCommon mode equivalent inductance LcmAnd common mode equivalent capacitance Ccm，Lcm＝LC+LD/2。
In the present invention, preferably, the differential mode equivalent circuit includes a differential mode interference source VDMCommon mode source impedance ZDMDifferential mode equivalent inductance LdmSum-and-difference mode equivalent capacitance Cdm，Ldm＝2LD+Lleak，Ccm＝2Cy， Cdm＝Cx+Cy/2。
In the present invention, preferably, an equivalent impedance of the LISN module in the common mode equivalent circuit is Z1, and a resistance value of Z1 is set to 25 Ω.
In the present invention, preferably, the LISN module has an equivalent impedance Z2 in the differential mode equivalent circuit, and the resistance value of Z2 is set to 100 Ω.
In the present invention, preferably, the noise separator is configured as a transformer separation network, and obtains two times of common mode signals or two times of differential mode signals by adjusting the polarity of the transformer in the transformer separation network.
The utility model has the advantages and positive effects that: an EMI power filter is a preferred tool for controlling conducted electromagnetic interference and radiated electromagnetic interference, the EMI power filter plays the role of two low-pass filters, common-mode interference and differential-mode interference are respectively attenuated, common-mode interference and differential-mode interference can be separated through mutual matching of an LISN module, a noise separator, tested equipment, a receiver and the EMI filter, EMI noise is effectively reduced, the LISN module is used for isolating power grid interference and providing stable test impedance, the noise separator is set to be a differential-mode suppression network, a power divider or a transformer separation network, a differential-mode suppression network is adopted to suppress a differential-mode part in EMI conducted interference, a user is enabled to measure common-mode interference characteristics, a preceding-stage common-mode filter is designed aiming at the common-mode interference, the common-mode filter is continuously modified to enable the common-mode interference to be reduced below a standard, and a subsequent-stage differential-mode filter is designed aiming at the rest differential-mode interference exceeding, the design is more flexible and convenient; the power divider can effectively separate common-mode signals and differential-mode signals from total EMI interference, and ensures that the common-mode signals and the differential-mode signals are effective in a frequency range specified by an EMC standard; by adopting the transformer separation network, double common-mode signals or double differential-mode signals can be obtained by adjusting the polarity of the transformer in the transformer separation network.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is a schematic block diagram of an EMI power filter of the present invention;
fig. 2 is a schematic block diagram of an EMI power filter with noise separator in accordance with the present invention;
fig. 3 is a schematic diagram of a differential mode suppression network according to a first embodiment of the EMI power filter of the present invention;
fig. 4 is a schematic diagram of a 0 ° power divider according to a second embodiment of the EMI power filter of the present invention;
fig. 5 is a schematic diagram of a 180 ° power divider according to a second embodiment of the EMI power filter of the present invention;
fig. 6 is a schematic block diagram of an EMI power filter with a power divider according to the present invention;
fig. 7 is a schematic diagram of a transformer separation network according to a third embodiment of the EMI power filter of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When a component is referred to as being "connected" to another component, it can be directly connected to the other component or intervening components may also be present. When a component is referred to as being "disposed on" another component, it can be directly on the other component or intervening components may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The first embodiment is as follows:
as shown in fig. 1 to 3, the present invention provides an EMI power filter, including a LISN module, a noise separator, a device under test and a receiver, the LISN module is used for providing stable line impedance, isolating power grid interference, coupling interference generated by the tested device to the receiver and preventing power grid voltage from being applied to the receiver, the receiver is used for analyzing the interference voltage of the corresponding frequency point, the tested equipment is connected between the live wire input end of the power grid and the zero line input end of the power grid through the LISN module, the LISN module is coupled to form a live wire interference voltage terminal and a zero line interference voltage terminal, the receiver is connected with the live wire interference voltage terminal and the zero line interference voltage terminal, the noise separator is arranged between the LISN module and the receiver and used for separating common mode interference and differential mode interference.
The LISN module, i.e., the line impedance stabilization network, is used to isolate grid interference and provide stable test impedance, so that the device under test (i.e., DUT) has an objective test environment in conducted emission testing. The LISN module mainly plays three roles: (1) providing a stable 50 ohm line impedance over the frequency range specified by the test standard; (2) isolating the power grid from the tested equipment; (3) coupling the interference generated by the device under test to the receiver and preventing the mains voltage from being applied to the receiver.
In this embodiment, the noise separator is further configured as a differential mode suppression network, the differential mode suppression network includes two resistors R1 and a resistor R2, one end of each of the two resistors R1 is connected to the LISN module, the other end of each of the two resistors R1 is connected in parallel and then connected in series with one end of the resistor R2, and the other end of the resistor R2 is connected to the receiver. Two input ends of the differential mode suppression network are connected with a live wire and a zero wire of the LISN module, an output end of the differential mode suppression network is connected with the connecting machine, interference measured by the differential mode suppression network is twice of common-mode voltage and does not contain differential-mode voltage, and therefore the actual common-mode voltage is a numerical value obtained after the voltage measured by the receiver is reduced by 6 dB.
In this embodiment, further, the resistance values of the two R1 are equal.
In this embodiment, further, an EMI filter is further included, and the EMI filter includes a common mode inductor choke LCDifferential mode inductance choke LDDifferential mode capacitor CxAnd a common mode capacitor CyThe equivalent simplification is carried out to a common mode equivalent circuit and a differential mode equivalent circuit, namely a common mode inductance choke coil LCHas a leakage inductance of Lleak。
Before and after the filter is connected between an interference source and a load, the ratio of voltage on load impedance is defined as the insertion loss of the filter, the insertion loss is the most key technical index of an EMI filter, and an insertion loss curve given by an attached use specification of the EMI filter on the market is measured according to the condition that the source impedance and the load impedance in a standard test system are both 50 omega. In practical application, the noise source and the load are changed along with the use environment, and the source impedance and the load impedance no longer satisfy a 50 Ω test system. Therefore, the EMI filter in the market cannot attenuate the EMI transmission interference according to the insertion loss curve given in the specification, and if the EMI filter is improperly used, the EMI filter cannot effectively suppress the interference, and even can amplify the interference signal. In design, it is necessary to make analytical measurements of the EMI conducted interferer impedance, taking into account the effect of the source impedance on the performance of the EMI filter.
The EMI filter can block or maximally attenuate the passing of high-frequency EMI disturbance, and can transmit useful signals to equipment without attenuation, so that the equipment is protected from electromagnetic interference. In practical application, the impedances presented by different electronic and electrical equipment and source networks of the filter are different, so that the impedance of the input end of the filter and the impedance of a disturbance source which need to be designed are arbitrary, and therefore, the impedance condition of the filter in the insertion loss measurement cannot be met. The attenuation of the disturbing signal by the EMI filter is not equal to the insertion loss given in the product description. However, if the selected filter network structure and parameters are reasonable and properly installed, higher insertion loss can be realized. The structure of the filter is selected according to the principle of impedance mismatch, the capacitor of the filter is connected in parallel with the high-impedance circuit, and the inductor of the filter is connected in series with the low-impedance circuit. If this principle can be followed, it can be ensured that the selected filter has the largest insertion loss at the same time as it has the largest reflection loss.
(1) Working under the condition that the source impedance is not matched with the load impedance, and the impedance of the source is changed from 1 omega to 100 omega; (2) the wide frequency spectrum of the interference source needs a high attenuation value of the filter from low frequency to ultrahigh frequency, the working state of components of the filter in a wide frequency band range is very complex, and the high-frequency characteristic of the filter is difficult to express by using the centralized parameters of inductive/capacitive elements; (3) the current amplitude of the electromagnetic interference source is changed greatly, which may cause the filter to generate saturation effect; (4) the EMI power filter should also minimize the consumption of the transmitted effective signal, but should have a large attenuation of the stopband unwanted signals to ensure that the interference energy of the conducted coupling is within a specified range.
EMI filters can be broadly classified into active filters and passive filters. The active EMI filter eliminates noise based on the concept of "reverse compensation", that is, electromagnetic interference is eliminated by injecting a current with the same amplitude and the opposite direction as the noise current into the interference path, but the performance of the active EMI filter is often limited by the operating bandwidth of the active device, and the high-frequency filtering effect is often not ideal. A conventional passive filter generally refers to an EMI filter consisting of discrete passive inductors and capacitors, where the common-mode capacitance C isyAnd common mode equivalent inductance LcmThe two components form a common mode filter for inhibiting common mode conducted noise, and a differential mode capacitor CxAnd a common mode inductor choke LCIs less thanleakTogether forming a differential mode filter. The EMI filter is relatively mature in technology and wide in application. The electromagnetic integration technology of the passive filter can modularize, miniaturize and integrate inductance and capacitance devices in the filter, effectively improve the power density of the filter and improve the high-frequency characteristic of the filter.
In the actual production process of the EMI filter, in order to achieve the optimal performance of the filter, it is necessary to: (1) the connection between the EMI filter and the interference source is made as close as possible; (2) the minimum 30 degrees is kept between the first turn and the last turn of the winding inductance to improve the self-resonant frequency; (3) the lead wire of the capacitor of the EMI filter is shorter as much as possible so as to reduce the equivalent parasitic inductance of the capacitor; (4) the input and output of the EMI filter are spaced as far apart as possible to minimize noise and radiative coupling between the filters.
The designed EMI filter is installed at the output end of the photovoltaic grid-connected inverter, interference can be effectively reduced to be below the standard after the EMI filter is added, and particularly the effect of interference suppression of the frequency band at 150K-10MHz is most obvious.
In this embodiment, further, the common-mode equivalent circuit includes a common-mode interference source VCMCommon mode source impedance ZCMCommon mode equivalent inductance LcmAnd common mode equivalent capacitance Ccm，Lcm＝LC+LD/2. The common-mode equivalent circuit mainly relates to a common-mode capacitor CyAnd a common mode inductor choke LCCalculating common mode equivalent capacitance C by using common mode equivalent circuitcmAnd common mode equivalent inductance LcmAnd then calculating to obtain the common mode capacitance CyAnd a common mode inductor choke LC. For safety reasons, there is a specified limit to leakage current, and the magnitude of the safe leakage current specified according to the device under test and the standard can be represented by the following formula: i2 pi f CcmAnd calculating the selectable maximum common-mode capacitance value by U, wherein f is the working frequency of the power supply 50Hz, and U is the power supply voltage 220V.
In this embodiment, further, the differential mode equivalent circuit includes a differential mode interference source VDMCommon mode source impedance ZDMDifferential mode equivalent inductance LdmSum-and-difference mode equivalent capacitance Cdm，Ldm＝2LD+Lleak，Ccm＝2Cy， Cdm＝Cx+Cy/2. In designing equivalent differential mode capacitance CxIn time, because of no safe leakage current, the equivalent differential mode capacitor C is needed to reduce the inductance valuexThe larger the value is, the better the value is, but after the differential-mode capacitance value is increased, the self-resonant frequency of the filter is reduced, and the interference amplification of the filter may be caused, so that the consideration needs to be made on the parameter value selection, and the proper differential-mode capacitance back root needs to be selectedAccording to
And calculating corresponding differential mode inductance values.
In this embodiment, further, the equivalent impedance of the LISN module in the common-mode equivalent circuit is Z1, and the resistance value of Z1 is set to 25 Ω.
In this embodiment, further, the equivalent impedance of the LISN module in the differential mode equivalent circuit is Z2, and the resistance value of Z2 is set to 100 Ω.
Example two:
as shown in fig. 4, 5, and 6, the difference from the first embodiment is that in the present embodiment, the noise separator is configured as a power divider, the power divider is configured as a 0 ° power divider and a 180 ° power divider, the 0 ° power divider is configured to sum a live interference voltage terminal and a neutral interference voltage terminal to obtain interference including a common-mode signal, and the 180 ° power divider is configured to subtract the live interference voltage terminal and the neutral interference voltage terminal to obtain interference including only a differential-mode signal. Because the differential mode suppression network can only measure the noise of common mode interference and cannot measure the differential mode interference, although the active differential amplification circuit can measure the differential mode interference noise, the bandwidth of the amplifier cannot reach the frequency range of EMC standard, namely 10-30 MHz; although the current probe can measure the differential mode interference noise, the measurement accuracy is not accurate, and the power divider can effectively separate the common mode signal and the differential mode signal from the total EMI interference and is effective in the frequency range specified by the EMC standard.
Example three:
as shown in fig. 7, the difference from the second embodiment is that, in the present embodiment, the noise separator is configured as a transformer separation network, and by adjusting the polarity of a transformer in the transformer separation network, a doubled common mode signal or a doubled differential mode signal is obtained.
The utility model discloses a theory of operation and working process as follows: through the mutual cooperation between the LISN module, the noise separator, equipment to be tested, receiver and EMI wave filter, can separate common mode interference and differential mode interference, effectively reduce EMI noise, the LISN module is used for providing stable line impedance, keep apart the electric wire netting and disturb, couple the interference that equipment to be tested produced to the receiver, prevent that the electric wire netting voltage from adding to the receiver, the receiver is used for the interference voltage size of analysis corresponding frequency point, it has equipment to be tested to connect through the LISN module between the live wire input of electric wire netting and the zero line input of electric wire netting, the LISN module coupling forms live wire interference voltage terminal and zero line interference voltage terminal, the receiver connects in live wire interference voltage terminal and zero line interference voltage terminal, the noise separator sets up between LISN module and receiver, be used for separating common mode interference and differential mode interference. The LISN module, i.e., the line impedance stabilization network, is used to isolate grid interference and provide stable test impedance, so that the device under test (i.e., DUT) has an objective test environment in conducted emission testing. The LISN module mainly plays three roles: (1) providing a stable 50 ohm line impedance over the frequency range specified by the test standard; (2) isolating the power grid from the tested equipment; (3) coupling the interference generated by the device under test to the receiver and preventing the mains voltage from being applied to the receiver. The noise separator is set as a differential mode suppression network, a power divider or a transformer separation network, the differential mode suppression network is adopted to suppress the differential mode part in EMI conducted interference, a user measures the common mode interference characteristic, a preceding-stage common mode filter is designed aiming at the common mode interference, the common mode filter is continuously modified to reduce the common mode interference to be below the standard, the remaining overproof part is the differential mode interference, and a subsequent-stage differential mode filter is designed aiming at the remaining overproof interference characteristic, so that the design is more flexible and convenient; the power divider can effectively separate common-mode signals and differential-mode signals from total EMI interference and is effective in a frequency range specified by EMC standards; by adopting the transformer separation network, double common-mode signals or double differential-mode signals can be obtained by adjusting the polarity of the transformer in the transformer separation network.
The embodiments of the present invention have been described in detail, but the description is only for the preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made within the scope of the present invention should be covered by the present patent.
Claims (10)
1. The EMI power filter is characterized by comprising an LISN module, a noise separator, a tested device and a receiver, wherein the LISN module is used for providing stable line impedance, isolating power grid interference, coupling interference generated by the tested device to the receiver and preventing power grid voltage from being applied to the receiver, the receiver is used for analyzing the interference voltage of a corresponding frequency point, the tested device is connected between a live wire input end of a power grid and a zero line input end of the power grid through the LISN module, the LISN module is coupled to form a live wire interference voltage terminal and a zero line interference voltage terminal, the receiver is connected to the live wire interference voltage terminal and the zero line interference voltage terminal, and the noise separator is arranged between the LISN module and the receiver and used for separating common mode interference and differential mode interference.
2. The EMI power filter of claim 1 wherein the noise separator is configured as a differential mode suppression network, the differential mode suppression network comprising two resistors R1 and a resistor R2, one end of each of the two resistors R1 being connected to the LISN module, the other end of each of the two resistors R1 being connected in parallel and in series with one end of the resistor R2, the other end of the resistor R2 being connected to the receiver.
3. The EMI power filter of claim 1, wherein the noise separator is configured as a power divider, and the power divider is configured as a 0 ° power divider and a 180 ° power divider, and wherein the 0 ° power divider is configured to sum the live interference voltage terminal and the neutral interference voltage terminal to obtain interference that includes the common-mode signal, and wherein the 180 ° power divider is configured to subtract the live interference voltage terminal and the neutral interference voltage terminal to obtain interference that includes only the differential-mode signal.
4. The EMI power filter of claim 2 wherein the two R1 values are equal.
5. The EMI power filter of claim 1 further comprising an EMI filter comprising a common mode inductor choke LCDifferential mode inductance choke LDDifferential mode capacitor CxAnd a common mode capacitor CyThe equivalent simplification is carried out to a common mode equivalent circuit and a differential mode equivalent circuit, namely a common mode inductance choke coil LCHas a leakage inductance of Lleak。
6. The EMI power filter of claim 5 wherein said common-mode equivalent circuit includes a common-mode interference source VCMCommon mode source impedance ZCMCommon mode equivalent inductance LcmAnd common mode equivalent capacitance Ccm，Lcm＝LC+LD/2。
7. The EMI power filter of claim 5 wherein said differential mode equivalent circuit includes a differential mode interferer VDMCommon mode source impedance ZDMDifferential mode equivalent inductance LdmSum-and-difference mode equivalent capacitance Cdm，Ldm＝2LD+Lleak，Ccm＝2Cy，Cdm＝Cx+Cy/2。
8. The EMI power filter as set forth in claim 5, wherein said LISN module has an equivalent impedance of Z1 in said common mode equivalent circuit, and a resistance value of said Z1 is set to 25 Ω.
9. The EMI power filter as set forth in claim 5, wherein said LISN module has an equivalent impedance of Z2 in said differential mode equivalent circuit, and a resistance value of said Z2 is set to 100 Ω.
10. The EMI power filter of claim 1 wherein the noise separator is configured as a transformer separation network, and wherein the double common mode signal or the double differential mode signal is obtained by adjusting the polarity of the transformer in the transformer separation network.
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| TWI805423B (en) * | 2021-06-28 | 2023-06-11 | 立錡科技股份有限公司 | Switching power converter and active emi filter circuit thereof |
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| TWI805423B (en) * | 2021-06-28 | 2023-06-11 | 立錡科技股份有限公司 | Switching power converter and active emi filter circuit thereof |
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Address after: 300000 Haitai green industrial base k2-2-502-a, No. 6, Haitai development road, Huayuan Industrial Zone, Binhai New Area, Tianjin Patentee after: TIANJIN BLJ TECHNOLOGY DEVELOPMENT Co.,Ltd. Address before: 300392 Haitai green industrial base k2-2-502-a, No. 6, Haitai development road 6, Huayuan Industrial Zone, Xiqing District, Tianjin Patentee before: TIANJIN BLJ TECHNOLOGY DEVELOPMENT Co.,Ltd. |