Power battery system, as a system which is closely combined with hardware and control system, can be roughly divided into two parts: battery testing and battery management system (BMS) testing. The following are the test results of these two parts.
1. Battery testing
Generally, the battery body is tested in DV/PV (design verification/production verification) stage to verify whether the design/production of the battery meets the design requirements. Including temperature test, mechanical test, external environment simulation test, low-voltage electrical test, electromagnetic compatibility test, electrical safety test, battery performance test, abuse test and so on. Because everyone is more concerned about battery safety, this paper mainly introduces the test method of battery abuse test:
1) acupuncture test
Simulate the scene that the battery is pierced by sharp instrument, because the penetration of foreign objects may lead to internal short circuit, and the test requires no fire or explosion.
2) salt water immersion
Long-term immersion test with 5% normal saline showed that the battery function was normal.
At present, the recommended waterproof and dustproof grade of battery packs for new energy vehicles is IP67 (that is, the battery packs of SAIC and Weilai are IP67 after being soaked in water with a depth of 1 meter for half an hour without damage). The use environment of cars is harsh, so it is not too much to do waterproof and dustproof protection (one year, heavy rain in Shanghai caused garage water accumulation, traditional cars were flooded, and electric cars were intact).
3) External fire:
Ignition duration at 590℃ 130 seconds, the battery has no explosion, fire, combustion and flame residue.
4) Fall:
1m freely falls on the steel plate, and the battery shell is intact and functions normally.
5) Vibration test
The high frequency vibration simulation test requires the battery pack to work normally. Colleagues who make battery packs should know that this is also difficult to pass.
2. Battery Management System (BMS) test
The testing of battery management system pays more attention to software testing, which is generally carried out in the process of software function development.
Different from the automatic driving system that has not been mass-produced, it is more inclined to use C language to realize software design. The mature software of electric vehicle control system (such as vehicle controller, motor controller and battery management system) is based on model-design software development. Compared with C, the advantage of MBD development is that it can express complex logic graphically, and its readability, portability and convenience of development and debugging are greatly enhanced. At the same time, the use of mature code generation tool chain also avoids the low-level errors that are easy to occur in manual code. Many tests are specified in model-based software development, such as MIL/SIL/HIL:
1) MIL(Model-In-Loops) is not only a model in-the-loop test, but also a verification of whether the software model can realize the software function. The test basis is the software requirements decomposed from the system requirements.
2) Test the Sil(Software-In-Loops) software in the loop, and compare whether the C code automatically generated by the model is consistent with the function realized by the model itself. You can use the tools provided by Simulink to test the Sil.
3) Test the PIL (Processor-in-Loops) processor in the loop, in order to test whether the automatically generated code deviates from the model in function realization after being written into the controller. PIL seems to be irrelevant, but ignoring it will also cause some bad consequences (such as scheduling problems, CPU load, stack overflow, etc.). )
4) HIL (Hardware-in-the-loop) hardware-in-the-loop test is used to test the complete system function of the controller. Generally, the test bench of the system where the controller is located will be built, and the electrical characteristics of sensors (such as temperature) and actuators (such as fan load) will be simulated with electrical components to verify the complete system function.
The use cases of these test links come from system requirements. In the process of automobile software development, development and testing are carried out in a V shape, which is usually called the V model of software development. Interested students can check the automotive software development process ASPICE.
In the process of unified development, the link of testing software is emphasized. You should know that the problem of mobile phone software is only a second, and the problem of car software affects people's life.
In the Toyota Brake Door Incident, the American government sent embedded software experts and computer professors from Carnegie Mellon University to inspect the software code of the engine control system in detail, and Toyota's abuse of global variables (tens of thousands) and confusion of software safety mechanism were severely punished. If Toyota had paid attention to software testing, this might not have happened.
Finally, come again & on the testing of parts in the extreme environment of the whole vehicle: the durability test of the whole vehicle is generally the test of the whole vehicle factory. The calibration engineer is responsible. The cost of automobile durability test is very high. The cost of building engineering prototype cars (about 654.38+0 million each), renting test sites and engineering teams tests the financial strength of manufacturers, and it is impossible to run without a strong cash pool. However, the more tests are carried out in extreme environments such as extreme cold, high temperature and high humidity, the more the function, performance and durability of the parts can be fully verified, and the earlier the problems are found, the lower the cost of solution and maintenance.
1. Low-temperature endurance test, which mainly tests cold start performance, is generally conducted in Heihe/yakeshi. The low-temperature charging and discharging ability, low-temperature protection strategy and battery heating function of the battery pack will be evaluated in this test.
2. The high-temperature durability test is generally conducted in Golmud. This paper mainly tests the charging and discharging ability of the battery pack at high temperature, the heat dissipation function of the battery pack and the overheating protection strategy. The picture below shows Weilai's high temperature test in Melbourne, Australia. Develop the whole vehicle at all costs.
3. Durability test in high temperature and high humidity environment is generally conducted in Hainan. Seawater environment will accelerate the corrosion of parts, and the durability of parts will be strictly tested. (Ps: Traditional cars also have an important plateau test, which mainly tests the performance of the engine at low air pressure. Electric vehicles generally do not need to carry out this test. )
If the battery pack is done well, it will promise that the battery will decay within its service life. For example, Weilai ES8 promises that the battery capacity attenuation will not exceed 20% when driving 300,000 kilometers 10. Everyone who develops batteries knows that it is very difficult to achieve this level. Dare to make a public commitment also shows that their battery durability test has reached a very good level.