Online electromagnetic interference filter attenuation test system

Abstract

The invention discloses an on-line electromagnetic interference filter attenuation test system. A noise injection device simulates an actual common-mode signal, amplifies noise and outputs the noise to a filter attenuation test device; the filter attenuation testing device comprises a to-be-tested EMI filter and a measuring device and is connected with the noise injection device, the filter load impedance simulation device is used for calculating impedance actually connected to load equipment and then extracting equivalent circuit parameters, and equivalent load impedance provided by a passive device is used for simulating port impedance of an actual filter. The online electromagnetic interference filter attenuation test system can solve the technical problem that in a traditional EMI filter attenuation test scheme, due to the fact that the two ends are both defaulted to be in 50-ohm matching, test is inaccurate, the provided online electromagnetic interference filter attenuation test system can directly test active equipment, and low-frequency noise signals can be injected into a filter to be tested under extremely small attenuation; it can be ensured that the high-frequency test injection loop flows to the to-be-tested filter, and reverse injection of part of the high-frequency test injection loop to the power amplification device is avoided.

Description

Technical Field

[0001] The invention relates to the field of electronic circuits, and in particular to an online electromagnetic interference filter attenuation test system. Background Art

[0002] EMI (electromagnetic interference) filters, whose function is to prevent the electromagnetic interference generated inside the power electronic equipment from being transmitted to other instruments or circuits, are usually composed of some passive electronic components such as capacitors and inductors. They are widely used in various power converters and power supply equipment because of their high efficiency in noise suppression.

[0003] The working principle of EMI filter is to filter the electromagnetic noise generated by capacitors and inductors according to the different impedance characteristics of noises of different frequencies. An important indicator of EMI filter is the noise attenuation ability of the filter, that is, insertion loss.

[0004] The existing EMI filter attenuation test methods are basically to design a set of test fixtures for the filter structure and use a vector network analyzer for testing.

[0005] Reference is made to Chinese patent CN202220705868.1, which discloses an EMI filter attenuation test fixture, including a base, a test plate and a clamping piece. The base is a metal piece. The test plate includes an insulating substrate layer located at the lower layer and a metal plate layer located on the insulating substrate layer. The test plate is installed at the upper end of the base, and the upper end of the test plate corresponds to the upper end of the base and is provided with a placement hole that passes through from top to bottom. The insulating substrate layers on the left and right sides of the placement hole extend into the placement hole, and the upper ends of the extensions on both sides of the insulating substrate layer are both provided with two conductive sheets at intervals along the front-to-back direction. The clamping piece is installed on the test plate, and the left and right sides of the test plate are both provided with test plugs electrically connected to the metal plate layer. The insulating substrate layer is embedded with a test circuit electrically connected to both the conductive sheet and the test plug. In this way, the line length between the test plug and the two conductive sheets on the same side can be reduced, effectively reducing the influence of the high-frequency distribution parameters of the test line on the EMI filter insertion loss test result, thereby improving the credibility of the test result.

[0006] Most of the existing EMI filter attenuation test methods use vector network analyzers (VNA) for measurement. The biggest problem is that when using a vector network analyzer to test the filter, the connection system of the measuring instrument is a 50Ω matching system, which means that the impedance connected to the four ports of the EMI filter is 50Ω. However, in the actual application scenario of the EMI filter, the impedance connected to the two ends of the filter is not 50Ω. The 50Ω matching system test assumption under the traditional solution will directly lead to a large error between the insertion loss we test and the actual insertion loss of the filter.

[0007] Secondly, in the actual application of EMI filters, the magnetic core in the inductor will gradually tend to saturation as the current increases, resulting in a direct decrease in the inductance of the EMI filter, which will directly affect its noise suppression performance. Traditional testing methods are all small signal tests, so they cannot reflect the actual attenuation performance changes of the filter during large signal transmission.

[0008] A series of attempts have been made at home and abroad to test the actual attenuation performance of EMI filters. Simulating the impedance at both ends of the actual filter by raising the noise source impedance and load impedance is an important means of testing non-50Ω systems. However, the current noise source impedance extraction is not very accurate, and the extracted impedance after changing the test environment is not applicable to the changed test environment.

[0009] Chinese patent CN202211320730.0 discloses an online test and calculation system for power filter insertion loss, including a simulation module, a measurement module and an interference module; the simulation module is used to simulate the actual installation environment for the power supply EMI filter to be tested; the simulation module includes an input impedance stabilization device and a power supply load impedance simulation device; the power supply load impedance simulation device is an equivalent circuit corresponding to the specific characteristics of the load in the actual installation environment, and the specific characteristics include: inductance value, capacitance value, resistance value, impedance value and impedance angle at the operating frequency; the measurement module is used to measure and calculate the amplitude of the interference signal on the input line and output line of the power supply EMI filter to be tested; the interference module is used to inject a low-frequency interference signal into the power line at the input end of the power supply EMI filter to be tested.

[0010] The Chinese patent CN202211320730.0 has developed a system for the filter attenuation test under large signals. However, the patent uses a transformer to inject large signals. Because of its parasitic capacitance and power size, the bandwidth used by the transformer becomes lower and the size of the transformer will be very large. Secondly, this patent only considers the attenuation test of the low-frequency part, and uses low frequency to derive high-frequency attenuation performance. Compared with the actual attenuation of the filter at high frequency, the error is larger. And the patent uses an impedance analyzer (LCR) to test the load impedance, and when the load is an active device such as a battery or other power supply, its impedance test method will no longer be applicable. In addition, using an instrument to directly test the filter performance under large signals also has great safety risks. Secondly, the direct isolation between the injection device and the filter is not considered during the measurement process, which will cause the test to be inaccurate. Summary of the invention

[0011] A series of simplified concepts are introduced in the Summary of the Invention, which are all simplifications of the prior art in the field, and will be further described in detail in the Detailed Description of the Invention. The Summary of the Invention of the present invention does not mean to attempt to define the key features and essential technical features of the claimed technical solution, nor does it mean to attempt to determine the scope of protection of the claimed technical solution.

[0012] The first technical problem to be solved by the present invention is to provide an online electromagnetic interference filter attenuation test system that can solve the technical problem of inaccurate testing caused by the default 50Ω matching at both ends in the traditional EMI filter attenuation test solution.

[0013] The second technical problem to be solved by the present invention is that while solving the above-mentioned first technical problem, the online electromagnetic interference filter attenuation test system provided by the present invention can directly test active devices (batteries, power supplies, etc.).

[0014] The third technical problem to be solved by the present invention is that while solving the above-mentioned second technical problem, it can realize the injection of low-frequency noise signals into the filter to be tested with extremely small attenuation, ensure that the high-frequency test injection loop flows to the filter to be tested, and avoid part of the high-frequency test injection loop from being reversely injected into the power amplifier device.

[0015] In order to solve the above technical problems, the present invention provides an online electromagnetic interference filter attenuation test system, comprising:

[0016] A noise injection device 1 is used to simulate the actual common mode signal noise amplification output to the filter attenuation test device 2;

[0017] The filter attenuation test device 2 includes an EMI filter 2.2 to be tested and a measuring device for measuring the filter attenuation performance, which is connected to the noise injection device 1

[0018] The filter load impedance simulation device 3 is used to calculate the impedance of the actual connected load device and then extract the equivalent circuit parameters, and use passive devices to provide equivalent load impedance to simulate the port impedance of the actual filter.

[0019] Optionally, the online electromagnetic interference filter attenuation test system is further improved, and the noise injection device 1 comprises:

[0020] A noise current generating device, for simulating a simulated noise signal that generates an actual common-mode signal and transmitting it to a power amplifier;

[0021] A power amplifier device, which amplifies the analog noise signal into a noise signal of a specified power and outputs it to the filter attenuation test device 2 via the high-frequency loop blocking device 1.2;

[0022] The high-frequency loop blocking device 1.2 is used to ensure that the noise signal passes through without loss, and at the same time block the signal injected by the filter attenuation test device from flowing into the power amplifier end.

[0023] Optionally, the online electromagnetic interference filter attenuation test system is further improved, and the filter attenuation test device 2 comprises:

[0024] RF current probe 2.1, for contactless connection to the EMI filter 2.2 to be tested;

[0025] Attenuation performance measuring device 2.3, which is used to measure the filter attenuation performance.

[0026] Optionally, the online electromagnetic interference filter attenuation test system is further improved, and the radio frequency current probe 2.1 is connected to both ends of the EMI filter to form a series test method.

[0027] Optionally, the online electromagnetic interference filter attenuation test system is further improved, and the attenuation performance measuring device 2.3 is a vector network analyzer or a spectrum analyzer.

[0028] Optionally, the online electromagnetic interference filter attenuation test system is further improved, and the filter load impedance simulation device 3 includes:

[0029] A load impedance measuring device 6, which is used to measure the impedance of the active device;

[0030] The actual impedance extraction device 8 calculates the load impedance of the actual test using a preset algorithm;

[0031] The load impedance fitting system 9 uses passive components to fit the measured actual load impedance, and connects the fitted circuit to the back end of the filter to complete the simulation of the input impedance of the filter load end.

[0032] Optionally, the online electromagnetic interference filter attenuation test system is further improved, and the load impedance measuring device 6 comprises:

[0033] Protection device 6.1, which is used to isolate the test equipment from the equipment under test;

[0034] An interface conversion device 6.2 converts the interface of the device under test into a port of the attenuation performance measurement device 2.3;

[0035] and, a load 7 to be tested.

[0036] Optionally, the online electromagnetic interference filter attenuation test system is further improved, and the protection device 6.1 is composed of a balun transformer for isolation and a DC isolation module.

[0037] Compared with the prior art, the present invention has at least the following technical effects:

[0038] 1. The present invention realizes the injection of low-frequency noise into the filter without affecting the actual attenuation performance test of the filter through the noise amplification module, and completes the impedance test and fitting of the active device under the premise of protecting the safety of the test instrument and the accuracy of the test results through the load impedance test and fitting device, and further completes the actual filter attenuation performance test by a pair of RF current probes. The attenuation performance test of the EMI filter under the simulation of the actual working condition is conducive to the evaluation of the attenuation of the actual working condition of the filter. The filter parameters can be pre-adjusted in the basic test to achieve the best attenuation performance before being installed in the equipment, which reduces the development cycle and cost of the entire equipment.

[0039] Compared with the traditional test scheme, the present invention solves the error caused by the idealization of the two ends of the EMI filter as a 50Ω system in the traditional test scheme and the difference between the test data and the actual application environment of the filter. The impedance test technology is used to test and fit the load end of the filter to make the impedance conform to the actual application environment, thereby obtaining accurate test results.

[0040] 2. The noise amplification module designed in the present invention has its own power supply and over-current and over-temperature protection module, and can basically meet the power reserve required in the filter attenuation test.

[0041] 3. Through the impedance test module with protection module, the impedance of active devices such as power supply and battery can be tested. This method is not only simple and easy to implement, but also can broaden the types of our test equipment and meet more filter working environments.

[0042] 4. The present invention can quickly complete the test of the common mode and differential mode impedance of the load by accessing the impedance test module through the vector network. The design is convenient and fast.

[0043] 5. The present invention adds an impedance extraction algorithm to the impedance test module to remove the effects of the protection module and the adapter module to complete the extraction of the impedance of the actual connected load, and its extraction error does not exceed 0.3Ω. The algorithm is simple and convenient, and only needs to obtain the information of the protection module and the adapter module. This algorithm makes the simulation of the actual connected impedance of the filter more accurate.

[0044] 6. The high-frequency loop blocking device designed in the present invention ensures the injection power of the low-frequency noise signal and the integrity of the high-frequency test signal at the same time. The insertion loss of the EMI filter attenuation test does not change before and after connecting to the power amplifier, thereby improving the reliability of the filter performance test.

[0045] 7. The present invention utilizes the design of connecting a vector network analyzer to a quick-release RF current probe to achieve accuracy and efficiency in repeated testing of EMI filter performance. The present invention can also convert the information measured by the current probe into impedance information, which is more beneficial to the actual performance analysis of the filter.

[0046] 8. The present invention uses online testing to clearly test that the insertion loss of the filter core gradually decreases as the current increases and gradually approaches saturation, and it is obvious that the insertion loss of the EMI filter tested when the current is distorted due to core saturation, such as Figure 5 shown.

[0047] 9. The present invention adopts two RF current probes which are easy to disassemble and install to test the attenuation performance of EMI filter in series at both ends of the filter, so as to quickly evaluate the attenuation performance of the filter. The test equipment with natural isolation of EMC current probe can effectively prevent the damage to the equipment during the test process. Its low transfer impedance also makes its application bandwidth very high, and the measured current can be converted into impedance through calculation.

[0048] 10. Traditional impedance test methods mostly use impedance analyzers (LCR) for measurement, but their biggest drawback is that they cannot directly test active devices such as batteries and power supplies, because the discharge moment may cause damage to the test instrument. The protection module designed in the present invention can test the impedance of active devices without changing the test accuracy and sensitivity, and extract the impedance of the actual test device through the measurement module.

[0049] 11. Since the frequency of low-frequency noise injected by the power amplifier is 1kHz-100kHz, and the frequency of the signal injected by the RF current probe can be as high as 100MHz, the present invention designs a high-frequency loop blocking device to allow the low-frequency noise signal to be injected into the filter with extremely small attenuation and ensures that the high-frequency test injection loop basically flows to the filter rather than partially being reversely injected into the power amplifier.

[0050] Figure 1 It is a schematic diagram of the structure diagram of the system of the present invention.

[0051] Figure 2 It is a schematic diagram of the circuit connection structure of the present invention.

[0052] Figure 3 This is a schematic block diagram of the impedance simulation device of the present invention.

[0053] Figure 4 This is a comparison diagram of impedance extracted by the load impedance extraction algorithm of the present invention.

[0054] Figure 5 Schematic diagram of filter insertion loss tested when current distortion occurs due to core saturation.

[0055] Description of Reference Numerals

[0056] Noise injection device 1

[0057] Power amplifier module 1.

[0058] High frequency circuit blocking device 1.2

[0059] Filter attenuation test device 2

[0060] RF Current Probe 2.1

[0061] EMI filter to be tested 2.2

[0062] Attenuation performance measurement equipment 2.3

[0063] Filter load impedance simulation device 3

[0064] Noise current generating device 4

[0065] Vector Network Analyzer 5

[0066] Load impedance measurement device 6

[0067] Protection device 6.1

[0068] Interface conversion device 6.2

[0069] Load to be tested7

[0070] Actual impedance extraction device 8

[0071] Load impedance fitting system9. DETAILED DESCRIPTION

[0072] The following is an explanation of the embodiments of the present invention by specific specific embodiments, and those skilled in the art can fully understand other advantages and technical effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through different specific embodiments, and the details in this specification can also be applied based on different viewpoints, and various modifications or changes can be made without deviating from the general design concept of the invention. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. The following exemplary embodiments of the present invention can be implemented in a variety of different forms and should not be interpreted as being limited to the specific embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present invention thorough and complete, and to fully convey the technical solutions of these exemplary specific embodiments to those skilled in the art. It should be understood that when an element is referred to as "connected" or "coupled" to another element, the element can be directly connected or coupled to another element, or there can be an intermediate element. The difference is that when an element is referred to as "directly connected" or "directly coupled" to another element, there is no intermediate element. In all figures, the same reference numerals always represent the same element. As used herein, the term "and / or" includes any combination and all combinations of one or more related listed items.

[0073] Embodiment:

[0074] refer to Figure 1 As shown, the present invention provides an online electromagnetic interference filter attenuation test system, comprising:

[0075] A noise injection device 1 is used to simulate the actual common mode signal noise amplification output to the filter attenuation test device 2;

[0076] Exemplarily, the noise injection device 1 mainly includes a noise current generating device 4, a power amplifying module 1.1 and a high-frequency loop blocking device 1.2.

[0077] The noise current generating device 4 generates a signal similar to the actual common mode signal noise by a signal generator and transmits it to the power amplifier input.

[0078] The power amplifier module 1.1 is used to amplify the simulated noise signal into a large signal with a certain power. The power amplifier is mainly composed of a series of resistors, capacitors and power transistors, including the power supply module of the power amplifier, the human-computer interaction module, and the input and output interface. The power amplifier is designed with its high power density, which reduces the development cost and improves the portability of the test. The power amplifier module 1.1 can optionally include an over-temperature and over-current protection module, which collects signals through its microcontroller unit (MCU) to feedback and control relays and fans for circuit protection and temperature control.

[0079] like Figure 2 As shown, the signal interface of the injection power amplifier module 1.1 adopts an N-type coaxial interface, and the impedance matching and high connection stability improve the stability of the system. The power supply module of the power amplifier adopts a three-wire interface of a traditional power supply with a built-in filter, and the other side adopts an aviation plug with a built-in lock to improve the stability of the power supply. The power amplifier panel 1.1 mainly includes over-current and over-temperature indicator lights and control buttons for the power amplifier. The power amplifier output 1.1 also adopts an N-type coaxial interface, and its maximum current can also meet the design requirements.

[0080] In the present invention, the output end of the power amplifier module 1.1 is connected to the high-frequency loop impedance device 1.2 via a coaxial cable, and an N-type coaxial interface is also used for input and output.

[0081] In order to illustrate the feasibility of the high-frequency loop blocking device 1.2, the following implementation methods in the prior art are given as examples. The corresponding implementation methods below should not be understood as limitations on the high-frequency loop blocking device 1.2. Existing technologies or self-developed devices that can ensure the lossless passage of noise signals and block the signal injected by the filter attenuation test device from flowing into the power amplifier device can be used in the present invention.

[0082] For example, referring to the principle of the Bias-tee device provided by the patent No. 202011501607.X, it is possible to realize the superposition of RF signals and DC signals while the impedance RF signal enters the DC end. The principle is to connect the inductor in series between the power amplifier output and the probe, and the capacitor in parallel at its two ends. By controlling the impedance of its capacitor and resistor, the low-frequency injected noise signal can pass losslessly while blocking the RF current probe 2.1 injection signal from flowing into the power amplifier module 1.1 end, ensuring that the signals transmitted by the probe and its power amplifier are all injected into the EMI filter 2.2 to meet the accuracy of its test. It should be noted that the PCB in the high-frequency loop blocking device 1.2 needs to be well grounded to the casing.

[0083] It should be noted that a short-circuit interface needs to be made at the output port of the high-frequency loop blocking device 1.2 to convert the four-port filter into a two-port device for easy testing. To ensure its power requirements, the short-circuit interface uses a high-temperature resistant, high-strength, and corrosion-resistant aluminum oxide copper busbar for connection. To match the filter interface, a replaceable short-circuit adapter is designed. The short-circuit interface uses a crimping buckle mode to improve its connection stability.

[0084] A filter attenuation test device 2, comprising an EMI filter 2.2 to be tested and a measuring device for measuring the filter attenuation performance, which is connected to a noise injection device 1;

[0085] Exemplarily, the filter attenuation performance measuring device 2 mainly includes a pair of quick-detachable RF current probe devices 2.1, an EMI filter to be tested 2.2, and an attenuation performance measuring device 2.3, which can be a spectrum analyzer or a vector network analyzer. Since the main concern is the common-mode signal, the single-ended signal output by the power amplifier is used to simulate the actual common-mode signal, which can reduce the cost of the test.

[0086] The quick-detachable radio frequency current probe device can be selected to have an air-gap magnetic core, which provides better anti-saturation capability than a closed magnetic core.

[0087] For example, the output of the RF current probe 2.1 is connected to a bidirectional N-type interface, which is fixed to the test box housing through a flange. It is worth noting that the interface of the test box is openable, which makes it convenient for us to clamp in and remove the probe, thereby improving the efficiency of the test. The other end of the test box is an N-type interface, which is directly connected to a vector network analyzer or a spectrum analyzer. The overall filter performance test box 2 is simple and efficient in design.

[0088] It should be noted that the test RF probe 2.1 is placed at both ends of the EMI filter in series. The method can convert the measured current attenuation change into the impedance of the actual filter through the corresponding algorithm, which is convenient for the subsequent filter optimization analysis. Since the test is a single port, it is necessary to test the four-port EMI filter 2.2 as a two-port device. By observing the change in the attenuation performance of the tested filter according to the change of the input signal, the actual attenuation performance of the filter in operation can be evaluated.

[0089] The present invention selects to adopt a detachable RF current test box 2.1, which improves the efficiency and stability of test repeatability. Its RF current probe with an air gap also prevents the problem of inaccurate test accuracy caused by saturation of the test instrument during the test of the EMI filter 2.2.

[0090] The filter load impedance simulation device 3 is used to calculate the impedance of the actual connected load device and then extract the equivalent circuit parameters, and use passive devices to provide equivalent load impedance to simulate the port impedance of the actual filter.

[0091] Exemplary, reference Figure 3 As shown, the filter load impedance simulation device 3 is connected to the entire test system through an N-type interface. This ensures the stability of the entire system connection. Secondly, the device interface of the entire system basically adopts an N-type port to ensure the consistency of the system. The filter load impedance simulation device 3 includes:

[0092] The load impedance measuring device 6 is mainly composed of a protection device 6.1, an interface conversion device 6.2 and a load to be tested 7. The protection device 6.1 is mainly composed of a balun transformer and a DC isolation module for isolation, and the main purpose is to isolate the test equipment from the equipment to be tested. The load impedance measuring device of the present invention can complete the measurement of the impedance of active devices such as batteries without reducing the measurement accuracy, providing a wider measurement range. The purpose of the interface adapter 6.2 is to convert the interface of the equipment to be tested into a port for instrument testing to achieve better mechanical matching. It should be noted that the setting of the adapter can be replaced accordingly according to the actual load interface requirements. The test range of load impedance is currently fixed at 1kHz-100MHz, and can be adjusted accordingly according to actual needs.

[0093] The adapter test port 6.2 of the load impedance extraction device 6 is changed to a replaceable structure, which is convenient for adapting to different test equipment. The protection device 6.1 for impedance testing is made of a PCB circuit board, wherein the ground of the protection device is in good contact with the impedance test outer box through a large copper plate, the input end of the interface of the protection device is in good contact with the adapter through a copper bus, and the output port is connected to the vector network analyzer for impedance testing through two N-type ports with flanges, and the N-type port is fixed to the test box shell through a flange.

[0094] like Figure 3 As shown, the actual impedance extraction device 8 of the present invention removes the effects of the protection device and the adapter through a series of calibration algorithms, and completes the extraction of the actual load impedance through calculation. The actual load impedance test effect is shown in FIG. Figure 4 .

[0095] In order to illustrate the feasibility of the actual impedance extraction device 8, the following implementations in the prior art are given as examples. The corresponding implementations below should not be understood as limitations on the actual impedance extraction device 8. The existing technology or self-developed algorithms that can calculate the actual test load impedance can be used in the present invention.

[0096] Refer to the impedance measurement calibration method in Section 4.3.3 of the Keysight Impedance Measurement Handbook, use the open-circuit short-circuit calibration and S-parameter matrix cascade method to calibrate the test parameters, and use the S-parameter impedance calculation formula to obtain the common-mode and differential-mode impedance of the device under test.

[0097] like Figure 3 As shown, the impedance fitting system 9 is based on the tested load impedance and builds a series of combined circuits of resistors, inductors and capacitors through parameter extraction to complete the test impedance fitting and meet the power requirements of the test.

[0098] In order to illustrate the feasibility of the load impedance fitting system 9, the following implementation methods in the prior art are given as examples. The corresponding implementation methods below should not be understood as limitations on the load impedance fitting system 9. The existing technology or self-developed devices or algorithms that can measure the actual load impedance and use passive devices to fit the input impedance of the filter load end can be used in the present invention.

[0099] The load impedance fitting system 9, referring to patent 202211174405.8, proposes a method for impedance fitting using passive devices, which can fit the tested load impedance using passive devices, calculate the corresponding capacitance, inductance and resistance values ​​according to the tested impedance, and combine the extracted values ​​in series and parallel through the existing device parameters so that the fitted load impedance is equal to the impedance of the device to be tested, connect the fitted circuit to the back end of the filter, and complete the simulation of the input impedance of the load end of the filter.

[0100] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. It will also be understood that, unless expressly defined herein, terms such as those defined in general dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and not interpreted in an ideal or overly formal sense.

[0101] The present invention has been described in detail above through specific implementation modes and embodiments, but these do not constitute limitations of the present invention. Without departing from the principles of the present invention, those skilled in the art may also make many variations and improvements, which should also be regarded as the protection scope of the present invention.

Claims

1. An online electromagnetic interference filter attenuation test system, characterized in that: include: A noise injection device (1) for simulating an actual common-mode signal noise amplification output to a filter attenuation test device (2); A filter attenuation test device (2), comprising a radio frequency current probe (2.1) to be tested, an EMI filter (2.2) to be tested and a measuring device for measuring the filter attenuation performance, which is connected to a noise injection device (1); The filter load impedance simulation device (3) is used to extract equivalent circuit parameters after calculating the impedance of the actual connected load device, and to simulate the port impedance of the actual filter by using passive components to provide equivalent load impedance.

2. The online electromagnetic interference filter attenuation test system according to claim 1, characterized in that: The noise injection device (1) comprises: A noise current generating device, for simulating a simulated noise signal that generates an actual common-mode signal and transmitting it to a power amplifier; A power amplifier device, which amplifies the analog noise signal into a noise signal of specified power and outputs it to the filter attenuation test device (2) via the high-frequency loop blocking device (1.2); The high-frequency loop blocking device (1.2) is used to ensure that the noise signal passes through without loss, and at the same time blocks the signal injected by the filter attenuation test device from flowing into the power amplifier end.

3. The online electromagnetic interference filter attenuation test system according to claim 1, characterized in that: The filter attenuation test device (2) comprises: A radio frequency current probe (2.1) for contactless connection to an EMI filter (2.2) to be tested; Attenuation performance measuring equipment (2.3), which is used to measure the attenuation performance of the filter.

4. The online electromagnetic interference filter attenuation test system as claimed in claim 3, characterized in that: The radio frequency current probe (2.1) is connected to both ends of the EMI filter to form a series test method.

5. The online electromagnetic interference filter attenuation test system as claimed in claim 3, characterized in that: The attenuation performance measurement device (2.3) is a vector network analyzer or a spectrum analyzer.

6. The online electromagnetic interference filter attenuation test system according to claim 1, characterized in that: The filter load impedance simulation device (3) comprises: A load impedance measuring device (6) for measuring the impedance of an active device; An actual impedance extraction device (8) calculates the load impedance of the actual test using a preset algorithm; The load impedance fitting system (9) uses passive components to fit the measured actual load impedance, and connects the fitted circuit to the back end of the filter to complete the simulation of the input impedance of the filter load end.

7. The online electromagnetic interference filter attenuation test system according to claim 6, characterized in that: The load impedance measuring device (6) comprises: Protective device (6.1), which is used to isolate the test equipment from the equipment under test; An interface conversion device (6.2) converts the interface of the device under test into a port of the attenuation performance measurement device (2.3); and, a load to be tested (7).

8. The online electromagnetic interference filter attenuation test system according to claim 7, characterized in that: The protection device (6.1) consists of a balun transformer for isolation and a DC isolation module.

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