Shaft current test structure and method for motor EMC (Electro Magnetic Compatibility) on-load test system

Abstract

The invention discloses a shaft current test structure and method for a motor EMC (Electro Magnetic Compatibility) on-load test system, which are based on a shaft current test structure with a test unit, test shaft current on a test shaft by using a current probe and obtain shaft current data through an EMI (Electro Magnetic Interference) receiver and a computer; the method is simple, convenient and rapid to operate and high in test efficiency, an existing motor EMC on-load test system does not need to be greatly changed, a current probe is adopted to test the shaft current, non-invasive measurement is adopted, and interference to normal operation of the system is reduced to the maximum extent; according to the invention, the problems that the current shaft current test method only focuses on the shaft current test of the motor itself, the comprehensiveness and reliability are poor, and the shaft current test requirement of the motor EMC on-load test system is difficult to meet can be effectively solved; the influence of the shaft current on the motor EMC on-load test can be explored, and the correlation degree and the action mechanism between the shaft current and the electromagnetic compatibility can be deeply analyzed and evaluated.

Description

Technical Field

[0001] The invention belongs to the technical field of measuring electric variables in physics, and in particular relates to a shaft current test structure and method for a motor EMC load test system. Background Art

[0002] The motor is one of the most important components in new energy vehicles. When the motor is working, it will generate electromagnetic interference to nearby electronic components, which can easily affect their normal operation. In order to ensure the safety and reliability of new energy vehicles, the motor needs to be tested for electromagnetic compatibility during the research and development process; the electromagnetic compatibility test of the motor relies on the motor EMC load test system, whose physical structure is a single-axis through-the-wall load test bench, including a gearbox and a receiving antenna arranged in an anechoic chamber. The input shaft of the gearbox is used to connect the motor, and the output shaft of the gearbox extends to the outside of the anechoic chamber through the through-the-wall shaft and is connected to the dynamometer. The dynamometer is used to provide a load for the motor. An EMI receiver is installed in the shielded room outside the anechoic chamber. The input end of the EMI receiver is electrically connected to the receiving antenna through a signal cable, thereby receiving and processing the electromagnetic interference generated by the motor.

[0003] When conducting electromagnetic compatibility tests on motors, the motors are prone to generate shaft voltage due to magnetic imbalance and static charge. When the shaft voltage is higher than the oil film breakdown voltage threshold, a shaft current will be generated in the closed loop formed by the motor shaft and various shaft system components. The presence of shaft current will seriously affect the accuracy of the test results, causing a large difference between the test results of the motor and the test results of the whole vehicle, and cannot reflect the electromagnetic radiation status of the motor in a real working environment. Therefore, in order to explore the influence of shaft current on the test, deeply analyze and evaluate the correlation and mechanism between shaft current and electromagnetic compatibility, it is necessary to test the shaft current of the motor EMC load test system. The commonly used shaft current test methods are the lead method, radio frequency method and additional bearing method. Whether it is the lead method that adds an insulating layer to the outer raceway and bearing chamber of the bearing and leads out the wire to measure the current, or the radio frequency method uses a receiving antenna with a specific bandwidth and undergoes a series of signal processing to quantify the frequency of shaft current, or the additional bearing method sets bearings with different functions inside and outside the motor and uses brushes to guide the current to achieve shaft current measurement, all of them are centered around the motor. When performing electromagnetic compatibility testing on the motor, in addition to the motor itself generating shaft current, the dynamometer as the motor's load device is also prone to generate shaft current during operation, and will enter the anechoic chamber with the shaft transmission parts and merge with the shaft current generated by the motor, which will not only affect the accuracy of the test results, but may even cause the background noise of the anechoic chamber to fail to meet the test standards. However, the commonly used shaft current test method is difficult to be directly used for the shaft current test of the motor EMC on-load test system itself. Therefore, it is necessary to design a new shaft current test method to fill the gap in the current shaft current test of the motor EMC on-load test system itself and improve the comprehensiveness of the shaft current test. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a shaft current testing structure and method for a motor EMC on-load test system, so as to solve the technical problem that the existing shaft current testing method is difficult to directly use for shaft current testing in a motor EMC on-load test system, and to achieve the effect of improving the comprehensiveness and reliability of the shaft current test.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The shaft current test structure for the motor EMC load test system comprises a gearbox arranged in an anechoic chamber, the gearbox is a shifting gearbox, the output shaft and the input shaft of the gearbox are respectively connected to a load unit and a test unit; the load unit comprises a dynamometer located outside the anechoic chamber, the dynamometer is connected to the output shaft of the gearbox through a through-wall shaft; the test unit comprises a test shaft located in the anechoic chamber, the outer cylindrical surface of the test shaft is smooth and conductive, one end of the test shaft is connected to the input shaft of the gearbox, and the other end is grounded through a conductive contact piece, the conductive contact piece is fixedly arranged and rotatably connected to the test shaft, an annular current probe is sleeved on the test shaft between the gearbox and the conductive contact piece, and the inner diameter of the current probe is larger than the diameter of the test shaft; a processing unit is arranged in a shielding room outside the anechoic chamber, and the processing unit is electrically connected to the current probe for obtaining shaft current data.

[0007] Furthermore, the anechoic chamber is also provided with a voltage probe electrically connected to the processing unit, and the voltage probe can be operated to respectively measure the shaft voltages on the dynamometer output shaft, the through-wall shaft and the measuring shaft.

[0008] Furthermore, the conductive contact piece is an annular carbon brush, and the inner side surface of the annular carbon brush abuts against and rotatably fits with the outer circumferential surface of the test shaft.

[0009] Furthermore, a support plate is fixedly provided below the annular carbon brush, a support rod is connected between the support plate and the annular carbon brush, the support plate is grounded, and the annular carbon brush is electrically connected to the support plate via a metal grounding belt.

[0010] Furthermore, a support seat which can slide axially along the test axis is provided on the support plate, and the current probe is connected to the support seat, and the current probe is coaxial with the test axis.

[0011] Furthermore, the difference between the inner diameter of the current probe and the diameter of the test shaft is greater than or equal to 10 mm.

[0012] Furthermore, the processing unit includes an EMI receiver and a computer. The EMI receiver is electrically connected to the current probe and the computer respectively. An attenuator is also electrically connected between the EMI receiver and the current probe.

[0013] The present invention also includes a shaft current test method for a motor EMC load test system, which is performed using the shaft current test structure as described above and includes the following steps:

[0014] 1) Adjust the gearbox gear position to match the speed and torque with the test conditions;

[0015] 2) Keep a certain distance between the inner side of the current probe and the outer surface of the test shaft;

[0016] 3) moving the current probe on the test shaft, and the processing unit respectively obtains shaft current data when the current probe is close to the gear box and close to the conductive contact;

[0017] 4) Repeat steps 1) to 3) to obtain shaft current data corresponding to various test conditions.

[0018] Furthermore, the end of the test shaft close to the gear box is the inner end, and the end close to the conductive contact is the outer end. In step 3), the corresponding shaft current data when the current probe is 50±5mm away from the inner end and 50±5mm away from the outer end are obtained respectively.

[0019] Furthermore, in step 3), when the processing unit obtains the shaft current data, the shaft current data with a bandwidth of 9kHz and a step size of 5kHz is taken in the frequency range of 0.15MHz-30MHz, the shaft current data with a bandwidth of 120kHz and a step size of 50kHz is taken in the frequency range of 30MHz-175MHz, and the shaft current data with a bandwidth of 1MHz and a step size of 500kHz is taken in the frequency range of 170MHz-245MHz.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The shaft current testing method of the present invention is based on the shaft current testing structure obtained by adding a test unit to the motor EMC load test system. A test shaft with a smooth outer cylindrical surface and no insulating coating is connected to the input shaft of the gear box through a coupling. The test shaft is grounded through an annular carbon brush, a metal grounding belt and a support plate to form a complete loop. The shaft current is tested on the test shaft using a current probe and the shaft current data is obtained through an EMI receiver and a computer. There is no need to make major changes to the motor EMC load test system. Not only is the test range wide, but the operation is simple and fast, and the test efficiency is high.

[0022] 2. The shaft current testing method described in the present invention uses a current probe to test the shaft current on the test shaft, which is a non-invasive measurement and minimizes interference with the normal operation of the system. The shaft current testing method described in the present invention can effectively solve the problems that the current shaft current testing method only focuses on the shaft current test of the motor itself, has poor comprehensiveness, and is difficult to meet the shaft current testing needs of the motor EMC load test system itself. It is conducive to exploring the influence of the shaft current size on the motor EMC load test, and in-depth analysis and evaluation of the correlation and action mechanism between the shaft current and electromagnetic compatibility.

[0023] 3. The test shaft voltage structure of the present invention can also use a voltage probe to perform shaft voltage tests on the output shaft of the dynamometer, the through-wall shaft located in the anechoic chamber and close to the first coupling (insulating coupling), and the test shaft. This not only ensures the accuracy and reliability of the test results, but also the test points are completely in the propagation path of the shaft current, thereby verifying the electromagnetic interference in the "propagation path" of the three elements of electromagnetic compatibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic top view of the shaft current test structure described in the embodiment;

[0025] Figure 2 It is a front view schematic diagram of the test unit described in the embodiment;

[0026] Figure 3 It is a flowchart of the steps of the shaft current testing method described in the embodiment;

[0027] Figure 4 It is a flowchart of the shaft voltage testing method described in the embodiment;

[0028] Among them, dynamometer 1, first coupling 2, first bearing seat 3, through-wall shaft 4, second bearing seat 5, second coupling 6, gearbox output shaft 7, gearbox 8, support plate 9, third coupling 10, test shaft 11, annular carbon brush 12, current probe 13, signal cable 14, anechoic chamber 15, attenuator 16, EMI receiver 17, computer 18, shielding room 19, load unit 20, support seat 21, support rod 22, processing unit 23, gearbox input shaft 24. DETAILED DESCRIPTION

[0029] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0030] Example:

[0031] See also Figure 1 and Figure 2, a shaft current test structure and method for a motor EMC load test system, the shaft current test method is performed based on the shaft current test structure, the shaft current test structure includes a gear box 8 arranged in an anechoic chamber 15, the gear box 8 is a shift gear box, the output shaft and input shaft of the gear box 8 are respectively connected to a load unit 20 and a test unit; the load unit 20 includes a dynamometer 1 located outside the anechoic chamber 15, the dynamometer 1 is connected to the gear box output shaft 7 through a through-wall shaft 4; the test unit includes a test shaft located in the anechoic chamber 15 11, the outer cylindrical surface of the test shaft 11 is smooth and conductive, one end of the test shaft 11 is transmission-connected to the gear box input shaft 24, and the other end is grounded through a conductive contact piece, the conductive contact piece is fixedly arranged and rotationally connected to the test shaft 11, an annular current probe 13 is sleeved on the test shaft 11 between the gear box 8 and the conductive contact piece, and the inner diameter of the current probe 13 is larger than the diameter of the test shaft 11; a processing unit 23 is provided in the shielding room 19 outside the radio wave darkroom 15, and the processing unit 23 is electrically connected to the current probe 13 for obtaining shaft current data.

[0032] In this embodiment, the input shaft of the dynamometer 1 is connected to the through-wall shaft 4 through the first coupling 2, the other end of the through-wall shaft 4 is connected to the gear box output shaft 7 through the second coupling 6, the gear box input shaft 24 is connected to the test shaft 11 through the third coupling 10, and the through-wall shaft 4 is close to the first coupling 2 and the second coupling 6, respectively, through the first bearing seat 3 and the second bearing seat 5 to provide support to ensure the stable rotation of the through-wall shaft 4.

[0033] In this embodiment, the anechoic chamber 15 also has a voltage probe (not shown) electrically connected to the processing unit 23, and the movable voltage probe measures the shaft voltages at the output shaft of the dynamometer 1, the through-wall shaft 4 and the measuring shaft 11 respectively.

[0034] See also Figure 1 and Figure 2 The conductive contact piece is an annular carbon brush 12, the inner diameter of the annular carbon brush 12 matches the diameter of the test shaft 11, and the inner side surface of the annular carbon brush 12 abuts against and rotates with the outer cylindrical surface of the test shaft 11; in this way, the annular carbon brush 12 with matching sizes is used to cooperate with the test shaft 11 so that the conductive contact piece maintains good contact with the surface of the test shaft 11.

[0035] See also Figure 1 and Figure 2A support plate 9 is fixedly provided below the annular carbon brush 12, a support rod 22 is connected between the support plate 9 and the annular carbon brush 12, the support plate 9 is grounded, and the annular carbon brush 12 is electrically connected to the support plate 9 through a metal grounding belt (not shown in the figure); in this embodiment, the support plate 9 is L-shaped, the support rod 22 is vertically connected to the horizontal section of the support plate 9, and a clearance hole for the test shaft 11 to pass through is opened on the vertical section of the support plate 9. The L-shaped support plate 9 is convenient for installing the motor and connecting with the gear box 8; the end of the test shaft 11 is grounded through the annular carbon brush 12, the metal grounding belt and the support plate 9 in sequence, so that the shaft voltage generated by the dynamometer 1 forms a complete closed loop through the annular carbon brush 12, the metal grounding belt and the support plate 9, so as to obtain shaft current data on the test shaft 11.

[0036] See also Figure 1 and Figure 2 A support seat 21 which can slide axially along the test axis 11 is provided on the support plate 9, and the current probe 13 is connected to the support seat 21, and the current probe 13 is coaxial with the test axis 11; in this way, the current probe 13 is coaxial with the test axis 11 through the support seat 21 and maintains a distance, which facilitates horizontal movement of the current probe 13 to adjust the test position.

[0037] See also Figure 1 and Figure 2 , the difference between the inner diameter of the current probe 13 and the diameter of the test shaft 11 is greater than or equal to 10 mm; in this way, when the shaft current on the test shaft 11 is measured by the current probe 13, it is convenient to keep a certain distance between the inner side of the current probe 13 and the test shaft 11, which can not only avoid the current probe 13 from hindering the rotation of the test shaft 11, but also avoid the danger caused by direct contact between the current probe 13 and the test shaft 11.

[0038] See also Figure 1 and Figure 2 The processing unit 23 includes an EMI receiver 17 and a computer 18, and the EMI receiver 17 is electrically connected to the current probe 13 and the computer 18 respectively; in this embodiment, an attenuator 16 is also electrically connected between the EMI receiver 17 and the current probe 13 for filtering processing, and the current probe 13 and the attenuator 16 are electrically connected through a signal cable 14.

[0039] See also Figure 3 Based on the shaft current test structure, the method of testing the shaft current using a current probe is as follows:

[0040] First, the ambient electromagnetic noise level of the anechoic chamber should be at least 6.0 dB lower than the limit value specified in the test plan. The shielding effectiveness of the shielded room must be sufficient to ensure that the relevant requirements for the ambient electromagnetic noise level can be met. The dynamometer should be isolated by insulation or filtering. In this embodiment, the first coupling adopts an insulating coupling to reduce the impact of the dynamometer on the relevant test results. The current probe method is used to measure the conducted disturbance of the shaft current. The parameters of the current probe used should meet the requirements of CISPR25:2016 with a frequency range of 10kHz-400MHz, a noise immunity of 3dB, and a bandwidth of 2MHz-400MHz. In this embodiment, the inner diameter of the current probe used is 40mm, the outer diameter is 80mm, the thickness is 19mm, and the transfer impedance is 5.6Ω.

[0041] The shaft current test structure is established based on the motor EMC load test system. During the test, all shielded high-voltage components should be grounded normally with low impedance, such as AN, cables, connectors and other devices. The dynamometer needs to be grounded, and all components of the test system need to be grounded and share the same ground with the dynamometer.

[0042] Then, check whether the connection of each component in the motor EMC load test system is reliable, replace the motor with a test shaft with a smooth outer surface and no insulating coating, use the third coupling to connect the test shaft to the gearbox input shaft, and rotate the annular carbon brush on the end of the test shaft away from the gearbox, and fix it with a support rod, and use a metal grounding strap to connect the annular carbon brush and the support plate to form a complete circuit.

[0043] Then, the dynamometer can rotate on its own, and the speed of the dynamometer and the gear position of the gearbox are adjusted to make the speed and torque at the test shaft match the test conditions; the initial condition is to maintain the speed at 1000r / min. To prevent damage to the equipment during the test, the speed is set to increase by 100r / min per second to reach the initial condition, and the initial condition is maintained for more than 1 minute. Check the working status of each component. If large-scale vibration and sharp abnormal noise occur, stop and check whether the gearbox input shaft and the test shaft are axially aligned.

[0044] Then, the current probe is moved by the support seat, and the processing unit obtains the shaft current data when the current probe is close to the gear box and close to the conductive contact piece respectively; in this embodiment, the end of the test shaft close to the gear box is the inner end, and the end close to the conductive contact piece is the outer end. In this step, the shaft current data corresponding to the current probe being 50±5mm away from the inner end and 50±5mm away from the outer end are obtained respectively; in this step, when the processing unit obtains the shaft current data, the shaft current data with a bandwidth of 9kHz and a step length of 5kHz is taken within the frequency range of 0.15MHz-30MHz, the shaft current data with a bandwidth of 120kHz and a step length of 50kHz is taken within the frequency range of 30MHz-175MHz, and the shaft current data with a bandwidth of 1MHz and a step length of 500kHz is taken within the frequency range of 170MHz-245MHz;

[0045] Finally, the above operation is repeated to obtain shaft current data corresponding to various test conditions. In this embodiment, the speed is increased by 1000 rpm each time according to the initial condition to reach the maximum speed, and the shaft current data after each speed change is obtained and saved.

[0046] The present invention is based on a shaft current test structure obtained by adding a test unit to a motor EMC load test system. A test shaft with a smooth outer cylindrical surface and no insulating coating is connected to the input end of the gear box through a third coupling. The test shaft is grounded through an annular carbon brush, a metal grounding belt and a support plate to form a complete loop. A current probe is used to test the shaft current on the test shaft, and the shaft current data is obtained through an EMI receiver and a computer.

[0047] The shaft current testing method for the motor EMC on-load test system of the present invention is simple and fast to operate, has high testing efficiency, does not require major changes to the existing motor EMC on-load test system, has a wide testing range, uses a current probe to test the shaft current, belongs to non-invasive measurement, and minimizes interference with the normal operation of the system; the adopted current probe has the characteristics of high bandwidth and high precision, can accurately and quickly capture the change of the shaft current, can meet the needs of high-frequency testing of the shaft current, and effectively reflect the dynamic change process of the shaft current; compared with the existing shaft current testing method, the present invention successfully fills the gap in the verification method of the influence of the shaft current of the motor EMC on-load test system itself on the electromagnetic compatibility test result of the motor; therefore, the shaft current testing method of the present invention can effectively solve the problem that the current shaft current testing method only focuses on the shaft current test of the motor itself, has poor comprehensiveness and reliability, and is difficult to better meet the shaft current testing needs of the motor EMC on-load test system, and is conducive to exploring the influence of the shaft current size on the motor EMC on-load test, and deeply analyzing and evaluating the correlation and action mechanism between the shaft current and electromagnetic compatibility.

[0048] See also Figure 4Based on the shaft current test structure, the method of testing the shaft voltage using a voltage probe is as follows:

[0049] First, use a voltage probe with a carbon brush. The carbon brush has excellent conductivity and outstanding wear resistance. Its soft characteristics enable it to form good electrical contact with the measured shaft under a certain pressure, which effectively ensures that the voltage signal can be smoothly transmitted from the measured shaft to the voltage probe. During the test, the carbon brush should be in close contact with the measured shaft.

[0050] Then, the carbon brush of the voltage probe is applied to the output shaft of the dynamometer, the position of the through-wall shaft located in the anechoic chamber and close to the first coupling (insulating coupling), and the test shaft, and the shaft voltage is tested at three points. When the carbon brush of the voltage probe is applied to the test shaft to test the shaft voltage, the annular carbon brush on the test shaft should be removed or the annular carbon brush should be separated from the metal grounding strip. Similarly, when the processing unit obtains shaft voltage data, shaft voltage data with a bandwidth of 9kHz and a step size of 5kHz are taken within the frequency range of 0.15MHz-30MHz, shaft voltage data with a bandwidth of 120kHz and a step size of 50kHz are taken within the frequency range of 30MHz-175MHz, and shaft voltage data with a bandwidth of 1MHz and a step size of 500kHz are taken within the frequency range of 170MHz-245MHz.

[0051] Finally, the above operation is repeated to obtain shaft voltage data corresponding to various test conditions. Similarly, in this embodiment, the speed is increased by 1000 rpm each time according to the initial condition to reach the maximum speed, and the shaft voltage data after each speed change is obtained and saved.

[0052] In addition, the EMI receiver and computer process and analyze the shaft voltage data measured by the voltage probe to obtain the shaft current conduction disturbance value in decibels (dB). The conversion formula between voltage and decibel is as follows:

[0053]

[0054] Among them, V is the actual voltage value to be converted, and Vref is the reference voltage value.

[0055] The method for testing shaft voltage described in the present invention uses a voltage probe to perform shaft voltage tests on three points: the output shaft of the dynamometer, the position of the through-wall shaft located in the anechoic chamber and close to the first coupling (insulating coupling), and the test shaft. This not only ensures the accuracy and reliability of the test results, but also the test points are completely in the propagation path of the shaft current, thereby verifying the electromagnetic interference in the "propagation path" of the three elements of electromagnetic compatibility; a voltage probe with a carbon brush is used to test the shaft voltage, and the soft and deformable characteristics of the carbon brush are utilized to enable it to have flexible contact characteristics, so that reliable contact can be achieved regardless of the shape and roughness of the shaft to be tested, and the carbon brush has a large contact area with the test piece and a low contact impedance, which can reduce the electromagnetic interference of the contact point and improve the accuracy of the test results; the shaft voltage is tested before the shaft current is tested, so as to obtain the shaft voltage before the shaft current is generated, and obtain the oil film breakdown voltage threshold of the system.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. The shaft current test structure for the motor EMC load test system is characterized by: The invention comprises a gearbox arranged in an anechoic chamber, the gearbox is a shifting gearbox, the output shaft and the input shaft of the gearbox are respectively connected to a load unit and a test unit; the load unit comprises a dynamometer arranged outside the anechoic chamber, the dynamometer is connected to the output shaft of the gearbox through a through-wall shaft; the test unit comprises a test shaft arranged in the anechoic chamber, the outer cylindrical surface of the test shaft is smooth and conductive, one end of the test shaft is connected to the input shaft of the gearbox, and the other end is grounded through a conductive contact piece, the conductive contact piece is fixedly arranged and rotatably connected to the test shaft, an annular current probe is sleeved on the test shaft between the gearbox and the conductive contact piece, the inner diameter of the current probe is larger than the diameter of the test shaft; a processing unit is arranged in a shielding room outside the anechoic chamber, the processing unit is electrically connected to the current probe for obtaining shaft current data.

2. According to claim 1, the shaft current test structure for the motor EMC load test system is characterized in that: The anechoic chamber is also provided with a voltage probe electrically connected to the processing unit, and the voltage probe can be operated to respectively measure the shaft voltages on the dynamometer output shaft, the through-wall shaft and the measuring shaft.

3. According to claim 1, the shaft current test structure for the motor EMC load test system is characterized in that: The conductive contact piece is an annular carbon brush, and the inner side surface of the annular carbon brush abuts against and rotates with the outer cylindrical surface of the test shaft.

4. The shaft current test structure for the motor EMC load test system according to claim 3 is characterized in that: A support plate is fixedly provided below the annular carbon brush, a support rod is connected between the support plate and the annular carbon brush, the support plate is grounded, and the annular carbon brush is electrically connected to the support plate through a metal grounding belt.

5. The shaft current test structure for the motor EMC load test system according to claim 4, characterized in that: A support seat which can slide axially along the test axis is arranged on the support plate, and the current probe is connected to the support seat, and the current probe is coaxial with the test axis.

6. The shaft current test structure and method for the motor EMC load test system according to claim 1, characterized in that: The difference between the inner diameter of the current probe and the diameter of the test shaft is greater than or equal to 10 mm.

7. The shaft current test structure and method for the motor EMC load test system according to claim 1, characterized in that: The processing unit comprises an EMI receiver and a computer. The EMI receiver is electrically connected to the current probe and the computer respectively. An attenuator is also electrically connected between the EMI receiver and the current probe.

8. A shaft current test method for a motor EMC load test system, characterized in that: The method is carried out using the shaft current test structure as described in any one of claims 1 to 7, comprising the following steps: 1) Adjust the gearbox gear position to match the speed and torque with the test conditions; 2) Keep a certain distance between the inner side of the current probe and the outer surface of the test shaft; 3) Move the current probe on the test shaft, and the processing unit obtains shaft current data when the current probe is close to the gearbox and close to the conductive contact; 4) Repeat steps 1) to 3) to obtain shaft current data corresponding to various test conditions.

9. The shaft current testing method for the motor EMC load test system according to claim 8, characterized in that: The end of the test shaft close to the gearbox is the inner end, and the end close to the conductive contact is the outer end. In step 3), the corresponding shaft current data when the current probe is 50±5mm away from the inner end and 50±5mm away from the outer end are obtained respectively.

10. The shaft current testing method for the motor EMC load test system according to claim 8, characterized in that: In step 3), when the processing unit obtains the shaft current data, the shaft current data with a bandwidth of 9kHz and a step size of 5kHz is taken in the frequency range of 0.15MHz-30MHz, the shaft current data with a bandwidth of 120kHz and a step size of 50kHz is taken in the frequency range of 30MHz-175MHz, and the shaft current data with a bandwidth of 1MHz and a step size of 500kHz is taken in the frequency range of 170MHz-245MHz.

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