What Tests Should the New Energy Vehicle Power Battery System Take?

February 22, 2022

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The power battery system is a system that combines the hardware ontology and the control system very closely. Its tests can be roughly divided into two parts: battery pack test (Pack) and battery management system (BMS) test. The test situation of these two parts is described below.



Battery Pack Test (Pack)


The battery pack test is generally carried out in the DV/PV (Design Verification/Production Verification) stage to verify whether the design/production of the battery pack meets the design requirements. Battery Pack Test includes temperature test, mechanical test, external environment simulation test, low-voltage electrical test, electromagnetic compatibility test, electrical safety test, battery performance test, abuse test, and more. The survey shows that the most concern of users is battery safety, so we mainly introduce the test method of battery pack abuse test:


1) Needle Puncture Test

Simulate the scene when the battery is pierced by a sharp object, because the foreign body may cause an internal short circuit, and the test requires no fire and no explosion.


2) Salt water immersion test

5% salt water immersion test for a long time, the battery function is normal.

At present, the recommended waterproof and dustproof rating of new energy vehicle battery packs is IP67 (that is, immersion in water 1 meter deep for half an hour without damage, such as SAIC and Weilai’s battery packs are IP67). The use environment of the car is harsh, and no matter how to do waterproof and dustproof protection, it is not too much.


3) External combustion test

590 degrees Celsius fire for 130 seconds, the battery does not explode, catch fire, burn and no flame remains.


4) Drop test

The battery case is fully functional when it falls freely on the steel plate at a height of 1m.


5) Vibration test

The high-frequency vibration simulation test requires the battery pack to function normally. According to feedback from technicians in the battery pack industry, this test is difficult to pass.


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Battery Management System (BMS) Testing


The test of the battery management system focuses more on software testing, which is generally carried out in the process of software function development. Unlike autonomous driving systems that have not yet been mass-produced, which tend to use C language for software design, today's mature electric vehicle control systems (such as vehicle controllers, motor controllers, and battery management systems) software are all Model-Based-Design (MBD). The advantages of MBD development compared to C language are that it can express complex logic in a graphical way, code readability, portability, and the convenience of development and debugging are greatly enhanced. At the same time, the use of a mature code generation tool chain also avoids low-level errors that are easily generated by manual code.

Several tests such as MIL/SIL/HIL are specified in the model-based software development link:


1) MIL (Model-In-Loops) is model-in-the-loop testing, which is to verify whether the software model can realize software functions. The test basis is the software requirements decomposed from the system requirements.


2) SIL (Software-In-Loops) software-in-the-loop test, compare whether the C code automatically generated by the model is consistent with the functions implemented by the model itself, and use Simulink's own tools to perform the Sil test.


3) PIL (Processer-In-Loops) processor-in-the-loop test, the purpose is to test whether the function implementation deviates from the model after the automatically generated code is written into the controller. PIL seems to be irrelevant, but not paying attention to it can cause some bad consequences (such as scheduling problems, CPU Load, stack overflow, etc.).


4) HIL (Hardware-In-Loops) hardware-in-the-loop test, to test the complete system function of the controller, generally build a test bench for the system where the controller is located, and use electrical components to simulate sensors (such as temperature) and actuators (such as fan load) electrical characteristics to verify complete system functionality.


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Test conditions of parts under the extreme environment of the whole vehicle


This part of the vehicle durability test is generally the responsibility of the test & calibration engineer of the OEM. The cost of the vehicle durability test is very large. The cost of building engineering prototypes (about 1 million yuan per vehicle), renting test sites, and engineering teams is a test of the manufacturer's financial strength. Without a strong capital pool, it cannot be run at all. However, the more tests are carried out in extreme cold, high temperature, high humidity and other extreme environments, the more fully the function, performance and durability of components can be verified. The earlier problems are found, the lower the cost of repairs.


1) Low temperature endurance test, mainly to test the cold start performance, generally carried out in extremely cold environmental conditions. The battery pack's low-temperature charge-discharge capability, low-temperature protection strategy, and battery pack heating function will all be assessed in this test.


2) The high temperature durability test is generally carried out in a high temperature environment. It mainly tests the charging and discharging capability of the battery pack at high temperature, the cooling function of the battery pack and the overheating protection strategy. The picture below shows NIO conducting a high-temperature test in Melbourne, Australia, at all costs for the development of the entire vehicle.


3) The high temperature + high humidity environment durability test is generally carried out in a humid and hot climate and seawater environment. The seawater environment will accelerate the corrosion of components, and the durability of the components will undergo strict tests.


(Ps: There is also an important plateau test for traditional vehicles, which mainly tests the performance of the engine under low pressure. Electric vehicles generally do not need this test.)


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