In general, high-voltage connectors are important parts of electric vehicles. This article gives a comprehensive and in-depth explanation of the development history of high-voltage connections, the technical characteristics of high-voltage connectors, and product verification tests. It is worth reading. 1 The development history of high-voltage connectors The development of high-voltage connectors for electric vehicles and the development of electric vehicles are carried out simultaneously. From the perspective of connectors, the development of domestic electric vehicle connectors has experienced the following generations. 1) The first generation of high-voltage connectors (Figure 1),
which started around 2008, were mainly derived from the remodeling of industrial connectors at that time. The characteristics of this generation of products are mainly metal connecting shells, no high-voltage interlocking function, and poor anti-mistaken insertion (anti-fool) effect. The more representative products are the metal connectors of the Amphenol HV series. Later, many connectors on the market were extended based on this type of product.
2) The second-generation high-voltage connector (Figure 2) adds a high-voltage interlock function on the basis of the first generation, and the housing of the connector gradually changes from metal to plastic.
3) The third-generation high-voltage connector (Figure 3),
plastic + shielding function + high-voltage interlocking high-voltage connector. The representative ones are the 800 series products in the industry (this type of product achieves part of the secondary unlocking function through the operation sequence, not a direct mechanical structure), such as TE/Amphenol/Smart Green and the new generation of domestic products.
4) The fourth-generation high-voltage connector (Figure 4),
plastic + shielding function + high-voltage interlock + secondary unlocked high-voltage connector. The representative ones are the 280 series products in the industry, such as TE/Smart Green and domestic new-generation products. This type of product achieves a secondary unlocking function through a mechanical structure, which is more secure.
5) The next generation of high-voltage connectors (Figure 5)
will consider cooling methods in the fourth generation of products, such as with high-power charging with liquid cooling and air cooling, to effectively increase the transmission energy density, reduce quality, and improve product overall performance . 2 Technical characteristics of high-voltage connectors for electric vehicles In the three-electric system of new energy vehicles, the high-voltage connection system has a pivotal position. It is like a vascular system that organically integrates all important organs in the human body. The battery has a positive and negative loop. Similar to the aorta and main vein of the human body, each system circuit is similar to the various arteries, veins and capillaries of the human body. It is an important guarantee for ensuring the energy transmission, safe and reliable operation of electric vehicles, and realizing continuous energy transmission to various systems. Figure 6
shows the relationship between the high-voltage connection system and Sanden.
2.1 Terminal type
At present, high-voltage connectors can be classified in two ways: terminal type and structure.
2.1.1 According to the terminal type (Figure 7)
1) Square terminal structure. Using stamped terminal technology, this type of terminal has low cost, mold requirements and high mold cost. It is widely used in small currents below 40A, and TE terminals are representative in the industry. Some Japanese and American car companies use square terminal structures for high-current connectors, such as Sumitomo and Yazaki, and car companies such as Tesla and Toyota. 2) Round terminal structure. Machined terminal technology is mainly used. The cost of the terminal is higher than that of the stamped terminal. However, due to the machined production method, there is no need or very low mold investment, and the initial investment of the terminal is less. The more representative products are TEHVA800 series and domestic mainstream product series. 2.1.2 According to the structure type (Figure 8)
The connector structure can be divided into plugs and sockets according to the installation method. The plugs can be divided into linear plugs and 90° right-angle plugs. Sockets and so on.
2.2 High Voltage Interlock High Voltage Interlock (HighVoltageInter-lock, HVIL for short), a safe design method for using low voltage signals to manage high voltage circuits. In the high-voltage system design, in order to avoid the arcing caused by the high-voltage connector being opened and closed during the actual operation, the high-voltage connector should generally have the "high-voltage interlock" function. For a high-voltage connection system with high-voltage interlock function, the power and interlock terminals during connection and disconnection should meet the following conditions: when the high-voltage connection system is connected, the power terminal is connected first, and the interlock terminal is connected afterwards; when the high-voltage connection system is disconnected , The interlock terminal is disconnected first, and then the power terminal is disconnected. High-voltage interlocks are often used in high-voltage electrical circuits, such as high-voltage connectors, MSDs, and high-voltage power distribution boxes. The connector with high-voltage interlock can be disconnected by the logic sequence of the high-voltage interlock when it is unlocked when the power is on. The disconnection time is related to the difference in the effective contact length between the high-voltage interlock terminal and the power terminal. It is related to the speed when disconnected. Normally, the response time of the system to the interlock terminal circuit is between 10 and 100ms. When the disconnection (unplugging) time of the connected system is less than the system response time, there will be a safety risk of live plugging and unplugging, and the second unlocking is In order to solve this disconnection time problem, under normal circumstances, the secondary unlocking can effectively control the disconnection time above 1s to ensure safe operation. 2.3 Secondary unlocking The secondary unlocking is divided into two ways, one is achieved through the operation sequence, which is achieved through the opposite or different direction from the normal pullout, such as the mainstream HVA800 and HVC800 series high-voltage connector products on the market. When the connector is pulled out, the power-assisted wrench is exactly opposite to the separation direction or not in the same direction to increase the response time when pulling out and achieve the secondary unlocking function. The other is a mechanical secondary unlocking function. When the connector is pulled out, it can only be pulled out to the position where the high-voltage interlock terminal is disconnected for the first time. In this state, the power terminal is still in effective contact. The high-voltage interlock terminal is separated and disconnected, and then the power terminal can be separated after a second operation, so as to realize the requirement of twice unlocking function. Compared with the operation sequence unlocking, the mechanical secondary unlocking has higher safety, but the structure Relatively more complicated. Figure 9 shows the secondary unlocking process.
2.4 Locking structure The secondary locking structure of the connector (Connector Position Assurance, CPA for short) is a buckle structure used to increase the strength of the connector locking device. CPA can effectively protect the reliable connection of connector plugs and sockets, and prevent accidental loosening or poor contact during the operation of the car. Meet the requirements of reliable locking. The working principle of CPA, when the main locking structure is locked, the CPA assists the locking. At this time, the main locking structure will not be easily affected by the external environment and loosen (except for the failure of the main locking structure). The CPA needs to be unlocked when unlocking. Normally unlocked, it can meet a kind of locking structure used under harsher conditions. 2.5 Terminal Auxiliary Structure Connector Terminal Position Assurance (TPA) (Figure 10) is a structure used for secondary protection and limiting of the terminal to prevent the terminal from coming out under the action of external tension. Causes the line to be interrupted, and is used in situations where the environment is harsh or requires greater pull-off force. This kind of structure generally includes two kinds of holding structures, one is the holding structure of the terminal itself, and the other is the holding structure composed of TPA.
2.6 Evaluation of key parameters for terminal crimping Terminal crimping is a key process at the core of the connector industry. Evaluation of the effect of terminal crimping mainly consists of the following points. 1) Terminal tensile strength. The evaluation of the effect of terminal crimping includes the minimum tensile strength of the crimping between the terminal and the wire. The main parameter requirements are shown in Table 1.2) Terminal resistance. Evaluating the effect of terminal crimping includes crimping resistance test evaluation. Table 2 shows the terminal resistance.
3) Analysis of terminal crimping profile. After crimping the effective area of the terminal crimping (select the densest compression area), cut, polish, and cut the end face, and then use professional equipment to test the compression ratio. The compressed cable is required when it is placed about 5 to 10 times. There is no visible gap between the copper wires, and the compression ratio should be controlled at 80%~90%. 4) Terminal temperature rise. The temperature rise test generally requires that the temperature rise does not exceed 55K (different standards correspond to different requirements, and there are also 50K). The requirement in the national standard GB/T37133-2018 is 55K. 6) Definition of terminal pressure high voltage width. For the terminal after the previous test is OK, define the terminal pressure height and pressure width, and perform CPK control during the manufacturing process. 2.7 Comprehensive testing of high-voltage connectors. High-voltage connectors and wiring harnesses need to be comprehensively tested for product performance during the off-line production process. This type of comprehensive testing plays a very important role in the quality of products, and generally includes but is not limited to the following Item to be tested. 1) Withstand voltage test. It is mainly aimed at whether there is a risk of poor withstand voltage due to changes in space or climbing distance during the assembly process, or the risk of poor withstand voltage caused by wire harness crimping or other damage caused during the wiring harness assembly process. Normally, this type of The test requires 100% inspection. 2) Insulation test. It is mainly aimed at whether there is a risk of poor insulation caused by changes in space or climbing distance during the assembly process of the product, or the risk of poor insulation caused by wire harness crimping or other damage during the wiring harness assembly process. 3) The loop is turned on. It is mostly used in 2 groups or more circuits to detect whether each circuit of the connector has a one-to-one correspondence after assembly. 4) Air tightness test. It is suitable for the test of finished connector or wiring harness assembly. The air pressure of 47.8kPa is applied to test the tightness of the connector. The test time, leakage value and other parameters can be adjusted according to the characteristics of the product. 5) Shielding loop test. It is used to detect the resistance value in the shielding circuit. Generally, the shielding resistance should be less than 10mΩ.
The comprehensive simulation test bench (Figure 11)
can realize the main electrical performance testing (insulation, withstand voltage, continuity, etc.) and air tightness test of the connector. When NG is detected, the comprehensive test bench program is locked and accompanied by the flashing of the alarm light. It needs to be opened by someone. After the test is OK, a unique barcode (two-dimensional code) label can be automatically generated and printed to ensure that all offline products are tested and traceable.
3 Test verification 3.1 Test system construction As the performance of the high-voltage connector is directly related to the safety of the entire new energy vehicle, the requirements for the product, in addition to obtaining the standard compliance report of the final product state, will also be in the design and production stages of the factory. There are DV test verification and PV test. The test requirements mainly include the following aspects. 1) Electrical performance. Electrical performance includes the confirmation of electrical parameters and the guarantee of electrical safety. Such as current circulation, ground resistance, insulation withstand voltage test, etc. 2) Mechanical properties. In order to ensure the convenience of product installation, the reliability of connection and the convenience of maintenance, requirements are made on the product's pulling force, vibration, and mechanical mechanism. 3) Environmental performance. Including salt spray resistance, thermal aging, temperature shock, damp heat cycle, etc., these environments can completely reproduce the harsh working conditions of the product during use, and provide an inspection basis for the reliability of the product during use. The specific test items are implemented with reference to Table 3. The test methods and requirements will vary according to the working conditions of the product.
In order to effectively test the high-voltage connector, the laboratory built a system for temperature rise test (Figure 12). The test system includes a DC constant current source, a data acquisition system, and a control unit. The DC constant current source provides the required current value for the tested sample, the data acquisition system collects the temperature value of each point of the tested sample and the ambient temperature, and the control unit is used to adjust the current value in the entire test system.
3.2 Test data analysis
3.2.1 Terminal retention
In this study, four connectors of the same type were tested for terminal retention. The wire diameter cross-sectional area is 4mm2, and the test results are shown in Figure 13.
As can be seen in Figure 13, for a product with a wire cross-sectional area of 4mm2, the terminal tensile strength can meet the minimum tensile strength requirements in Table 1, and the product consistency between the male and female ends is within a controllable range. 3.2.2 Temperature rise In this study, a connector with a cable cross-sectional area of 4mm2 was selected, and the current value was 30A. The temperature rise data was recorded every day for 1008 hours, as shown in Figure 14.
Analyzed from Figure 14, the 4mm2 connector can withstand 30A for a long time, and the temperature rise is maintained within the range of 45K. In the first 600 hours, the temperature rise data fluctuates within a certain range. From 650 to 700 hours, the temperature rise value begins to rise to the highest value and gradually stabilizes at 45K, which can meet the basic operating conditions. As we all know, in new energy vehicles, the use environment of high-voltage connectors is more complicated. Humidity and temperature are the main factors that affect their performance. Therefore, when conducting verification tests, in addition to the verification tests in the normal temperature environment mentioned above, it is also necessary Carry out verification in a complex environment to ensure its reliability. 4 Conclusion High-voltage connection system is an important part of new energy vehicles, and its reliability issues will directly affect the safety of electric vehicles and will have a serious impact on the development of the industry. This paper studies the development history of high-voltage connectors for electric vehicles, focusing on the technical characteristics and test requirements of the products. Based on its key technical requirements, a comprehensive simulation test bench was built, a designated product was tested, and the test data was analyzed and summarized. The subsequent verification test needs to consider more complex environments to improve product reliability.