Analysis of the Rectification of Electromagnetic Radiated Emission Performance of a Plug-in Hybrid Mini Truck

The EMC radiated emission performance of the plug-in hybrid mini truck shall meet the relevant requirements of national standards GB/T 18387-2017 and GB 34660-2017 on the radiation of vehicles. The plug-in hybrid mini truck is placed in a 10 m semi-anechoic chamber for the whole vehicle as required by the standards. By activating different working conditions of the vehicle, various possible situations occurring in the normal driving process of the vehicle are simulated. When a plug-in hybrid mini truck underwent the above two tests, the result of radiated emission test was found to exceed the limit value of the standard. The relevant problem electrical parts are identified by analyzing the radiated emission data of the vehicle, conducting near-field scanning of the vehicle, and locating the over-standard problem points. Through rectification and optimization, the plug-in hybrid mini truck fulfilled the relevant requirements of national standards GB/T 18387-2017 and GB 34660-2017 on the radiation of vehicles.


Introduction
The continuous upgrading of electric vehicle technology has influenced the R&D route of mini trucks.By drawing on the mature electrification cases in passenger cars, OEMs began to develop electric mini trucks, and plug-in hybrid mini trucks also came into the market.Since there are fewer application cases of electrification in mini trucks, various problems arise during the development.To compete for the market and expand their market share, OEMs put more and more electrical parts in mini trucks to improve the operability and comfort of the driver, which leads to more and more serious EMC radiated emission problems in the vehicle.
Therefore, the government authority included the requirements of EMC radiated emission performance of plug-in hybrid mini trucks in the national standards GB/T 18387-2017 Limits and Test Method of Magnetic and Electric Field Strength from Electric Vehicles and GB 34660-2017 Road Vehicles-Requirements and Test Methods of Electromagnetic Compatibility to avoid the impact of plug-in hybrid mini trucks on the environment and to verify whether the EMC radiated emission performance of newly developed models meet the requirements of the standards, like this in [1,2].
This paper introduces the test scheme of electromagnetic radiated emission performance of a plug-in hybrid mini truck.According to the test scheme, the test data is analyzed, and the over-standard problem electrical parts are identified, rectified, optimized and verified, thus completing the EMC rectification and optimization of the HV system of the vehicle.

Test Site
According to the requirements of the national standards GB/T 18387-2017 Limits and Test Method of Magnetic and Electric Field Strength from Electric Vehicles and GB 34660-2017 Road Vehicles-Requirements and Test Methods of Electromagnetic Compatibility, the radiated emission test of the vehicle is conducted in the 10 m semi-anechoic chamber, as shown in Figure 1.

Test Procedure
The test procedure of GB/T 18387-2017 Limits and Test Method of Magnetic and Electric Field Strength from Electric Vehicles is: The vehicle under test is placed in the 10 m semi-anechoic chamber, and the electric field monopole antenna and magnetic field loop antenna are arranged at least 3 m from the four sides of the vehicle under test.The test frequency band is 150 KHz-30 MHZ.According to the test procedure, before the test, the vehicle shall run at a constant speed of 40 Km/h to take a pre-scan of the electric field in four directions: front, back, left, and right.And a pre-scan of the magnetic field in four directions are: front, back, left and right, with two polarization modes.After the pre-scan, the maximum surface of electric field radiation and the maximum surface of magnetic field radiation of the vehicle are identified by comparing four sets of data on the electric field and eight sets of data on the magnetic field, respectively.Finally, the vehicle takes the final scan at the maximum emitting surfaces of the electric field and magnetic field at the speed of 16 Km/h and 70 Km/h, respectively.The final scan data includes two sets of electric field data and two sets of magnetic field data with different polarization modes.
After the test, the final scan test data are compared with the electric and magnetic field limits in GB/T 18387-2017.If the limit value is exceeded in one of the waveform curves, the vehicle test is not passed.
The test procedure of GB 34660-2017 Road Vehicles -Requirements and Test Methods of Electromagnetic Compatibility test process is: The vehicle under test is first placed in the 10 m semi-anechoic chamber, and the radiated emission receiving antenna specified in GB 34660 is aligned with the center point of the vehicle by adjusting the vehicle position.Radiated emissions specified in GB 34660 are subject to narrowband and broadband tests, and the test frequency band is 30 MHZ-1 GHZ.During the narrowband test, all LV electrical parts of the plug-in hybrid mini truck shall be activated, such as the fan, wipers, headlamps, etc.For the broadband test, the working condition of 40 Km/h is added for the plug-in hybrid mini truck in addition to the narrowband working condition.Narrowband and broadband tests shall be conducted on the left and right sides of the vehicle, respectively, in vertical and horizontal polarization modes.
After the test, the four curves of the narrowband obtained from the test are compared with the narrowband limits of radiated emission specified in GB 34660-2017.The four curves of the broadband are compared with the broadband limits in the standard.If one of the waveform curves exceeds the limit, the vehicle test is not passed.

Analysis of Test Data
According to the above test scheme, a plug-in hybrid mini truck is tested per the two standards to obtain the vehicle test data.Figure 2 shows the test results of GB/T 18387-2017, where Figure 2

Investigation and Positioning of Problem Points
Over-standard EMC radiated emission of the vehicle may result from the operation of one or more controllers/actuators of the vehicle.According to the controller/load band corresponding to the over-standard EMC radiated emission, combined with the working condition of the vehicle (with-speed state, READY state, ON state, ACC state, OFF state) and the near-field scanning by a handheld spectrum analyzer, the problem parts of EMC are finally determined, like this in [3].
By near-field scanning of the motor electric control system, it is found that the radiation values of 16 MHZ and 20-30 MHZ of the motor electric control system are greatly enhanced relative to the noise floor.As shown in Figure 4, the handheld spectrum analyzer conducts the near-field scanning of the motor electric control system.
Through the near-field scanning of the vicinity of the LV harness port of the generator controller, a waveform curve that matches the over-standard point of GB 34660-2017 is found, and the generator controller is the main problem part causing the over-standard problem near 80 MHZ as per GB 34660-2017.As shown in Figure 5, the handheld spectrum analyzer conducts the near-field scanning of the vicinity of the LV harness port of the generator controller.Summary of the investigation: (1) The vehicle HV system leads to the over-standard problem at 10-50 MHZ as per GB/T 18387-2017 and GB 34660-2017, and the motor electric control system is the main problem part.
(2) Through the near-field investigation, it is found that the generator controller causes the over-standard problem near 80 MHZ as per GB 34660-2017.

Rectification and Optimization
The EMC problem in an automobile occurs when three elements of EMC coexist, i.e., source of disturbance, coupling path, and sensitive equipment.The coupling paths can include conduction coupling disturbance and radiation coupling disturbance.The disturbance transmitted along the conductor is called conduction disturbance, and it is transmitted by means of electric, magnetic, and electromagnetic coupling.The electromagnetic disturbance transmitted through space through electromagnetic waves is called radiation disturbance.It is transmitted by means of near-field induction coupling and far-field radiation coupling.Moreover, conduction and radiation disturbances may exist simultaneously, resulting in a compound disturbance.In the test, the vehicle is the source of disturbance; the EMC test room (10 m semi-anechoic chamber) space is a coupling path, and the vehicle transmits disturbance outward through space radiation coupling; the receiving antenna of the test room is sensitive equipment.As shown in Figure 6.In this regard, the rectification route of the vehicle EMC is shown in Figure 7 below, including suppressing the source of disturbance, cutting off the disturbance paths and reducing the sensitivity of the sensitive source.For radiated emissions, after the electromagnetic disturbance from the source of disturbance is radiated into space via the antenna, it will be received in space by the antenna of the sensitive device.The sensitive device is then influenced, which forms electromagnetic radiation coupling.
The impact of electromagnetic radiation coupling depends mainly on the following factors: (1) Voltage and current of the source of the disturbance.The greater the voltage power supply is, the faster the change over time is, and the greater the energy radiated out; (2) There are transmitting antenna's characteristics of the disturbance source, such as the area of the circuit loop and the geometric length of the antenna.The larger the area of the loop is, the greater the length is, and the easier the energy radiated out; (3) There are characteristics of the receiving antenna of the sensitive equipment, such as the area of the circuit loop and the geometric length of the antenna.The larger the area of the loop is, the greater the length is, and the easier it is to receive electromagnetic waves from space.
Resonance occurs when the signal is transmitted through the conductor.Resonance is most severe when the length of the harness is exactly an integer multiple of the half-wavelength of the signal.In general, when the length of the harness is greater than one-tenth of the signal wavelength, the signal's energy will be radiated to space through the harness.
The disturbance voltage U generated by electromagnetic radiation coupling is related to the magnitude of the disturbing electromagnetic field and the receiving function heff of the receiving antenna of the sensitive equipment, as shown in Figure 8.For radiated emission, the source of disturbance is mainly the vehicle controller/load and its harnesses, the disturbance path is mainly the space of the test room, and the sensitive equipment is the antenna of the test room.Since the harness itself does not generate disturbance, to further clarify the three elements of EMC, it can be considered that the source of disturbance is the vehicle controller/load, the disturbance path is the vehicle harness and the space of the test room, and the sensitive equipment is the antenna of the test room.
Because the space and antenna of the test room are the standard test environment, they cannot be changed.The requirements of EMC standards can be met only by rectifying the vehicle controller/load and harnesses.

Rectification of Problem Electrical Parts (1) Rectification of motor electric control system
By inspection, it is found that the 360° ring joint at the three-phase line port of the motor electric control system is unreliable, posing the risk of a false connection of the shielding layer, like this in [4].
As shown in Figure 9, the recommended grounding method for the HV harness shielding layer is: As shown in Figure 10, actual HV harness connection and optimization of the vehicle is: (2) Rectification of resolver line of motor electric control system The resolver line of the vehicle's drive motor is too long, and the grounding of the shielding layer of the connecting section of the resolver line is not reasonable.Therefore, the shielding of the resolver line is strengthened by copper foil wrapping, and the filtering magnetic ring is added inside to reduce outward radiation.As shown in Figure 11, a magnetic ring is added for filtering at the motor end of the resolver line, and the magnetic ring is fixed inside the shielding layer.As shown in Figure 12, copper foil is used to strengthen the shielding of the resolver line.As shown in Figure 13, the resolver line is changed to be arranged on the right side of the vehicle in order to reduce the circuit area of the resolver line.Figure 12.Rectification of Resolver Line 2.
(3) Rectification of excess harness of the motor electric control resolver line The harness of the electric control resolver and the harness of its connector are suspended inside the vehicle, forming an antenna, like this in [5].
As shown in Figure 14 and Figure 15, the excess harness is recommended to be wound in the following manner:  (4) Rectification of three-in-one controller housing and generator By analyzing the adhesive strip between the three-in-one controller housing and the cover, it is found that the role of the adhesive strip is to prevent water, which is not conductive.Therefore, the 3-in-1 controller housing is not a good metal confinement space, and there is a risk of electromagnetic leakage, so its shielding shall be enhanced.Due to the excessive outward radiation of the generator controller, filtering + reinforced shielding are adopted for optimization like this in [6].In addition, the filtering magnetic ring is added to the generator controller's HV harness, and the copper foil wrapping is adopted to strengthen the shielding.Finally, absorbing material is used for wrapping to further reduce its outward radiation like this in [7].Accordingly, the shielding was reinforced with copper foil between the three-in-one housing and the cover, as shown in Figure 16.The generator controller harness is wrapped by absorbing material, as shown in Figure 17.

Verification of Rectification
In the 10 m semi-anechoic chamber, the hybrid mini truck is tested in accordance with the requirements of GB/T 18387-2017 and GB 34660-2017 on the radiated emission performance index of the vehicle, like this in [8]- [10].By analyzing the test data, the radiated emission performance of the hybrid mini truck after rectification and optimization meets the standard requirements.Figure 18 shows the test results of GB/T 18387-2017, where Figure 18

Conclusion
In this paper, the test method of the plug-in hybrid mini truck is introduced by analyzing the requirements of the national standards GB/T 18387-2017 Limits and Test Method of Magnetic and Electric Field Strength from Electric Vehicles and GB 34660-2017 Road Vehicles -Requirements and Test Methods of Electromagnetic Compatibility on the radiated emission performance index of the vehicle.The methods of analyzing the over-standard data of the radiated emission test and locating the problem electrical parts in the process of the EMC mandatory test of a hybrid mini truck are elaborated.Finally, an EMC rectification and optimization case for the HV system of the vehicle is proposed.
During the rectification and optimization of the over-standard problems of the EMC radiated emission of the vehicle, it is found that part of the problems can be solved in the development stage of the EMC performance of the vehicle, such as excess harness, harness arrangement, shielding performance of the HV system housing, etc.We suppose the EMC performance index requirements
(a) shows the electric field test (at a vehicle speed of 70 Km/h) specified in GB/T 18387-2017, and Figure 2(b) shows the magnetic field Y-direction test (at a vehicle speed of 70 Km/h) specified in GB/T 18387-2017.Figure 3 shows the test results of GB 34660-2017, where Figure 3(a) shows the narrowband test in the left-side vertical direction specified in GB 34660-2017, and Figure 3(b) shows the broadband test in the left-side vertical direction specified in GB 34660-2017.(a) Electric Field (70 Km/h) Specified in GB/T 18387-2017 (b) Magnetic Field Y-direction (70 Km/h) Specified in GB/T 18387-2017 Figure 2. Test Results of GB/T 18387-2017 before Rectification.(a)Narrowband Test in Left-side Vertical Direction Specified in GB 34660-2017 (b) Broadband Test in Left-side Vertical Direction Specified in GB 34660-2017 Figure 3. Test Results of GB 34660-2017 before Rectification.By analyzing the vehicle test data, it is found that the over-standard point is 16 MHZ and 20-30 MHZ for the electric field and 16 MHZ for the magnetic field as tested under GB/T 18387-2017 Limits and Test Method of Magnetic and Electric Field Strength from Electric Vehicles; and 30-50 MHZ and 80 MHZ as tested under GB 34660-2017 Road Vehicles -Requirements and Test Methods of Electromagnetic Compatibility.

Figure 4 .
Figure 4. Near-field Scanning of Motor Electrical Control System.

Figure 9 .
Figure 9. Recommended Grounding Method of Shielding Layer.

Figure 10 .
Figure 10.Auxiliary Shielding with Copper Foil against Unreliable 360° Grounding of HV Harness Shielding Layer.

Figure 14 .
Figure 14.Recommended Folding Method for Excess Harnesses.

Figure 15 .
Figure 15.Resolver Line Folding and Copper Foil Wrapping.
(a) shows the electric field test (at a vehicle speed of 70 Km/h) specified in GB/T 18387-2017, and Figure 18(b) shows the magnetic field Y-direction test (at a vehicle speed of 70 Km/h) specified in GB/T 18387-2017.Figure 19 shows the test results of GB 34660-2017, where Figure 19(a) shows the narrowband test in the left-side vertical direction specified in GB 34660-2017, and Figure 19(b) shows the broadband test in the left-side vertical direction specified in GB 34660-2017.(a) Electric Field (70 Km/h) Specified in GB/T 18387-2017 (b) Magnetic Field Y-direction (70 Km/h) Specified in GB/T 18387-2017 Figure 18.Test Results of GB/T 18387-2017 after Rectification.(a) Narrowband Test in Left-side Vertical Direction Specified in GB 34660-2017 (b) Broadband Test in Left-side Vertical Direction Specified in GB 34660-2017 Figure 19.Test Results of GB 34660-2017 after Rectification.