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Why Battery Management System is Difficult to Break Through as a Technical Problem of New Energy Vehicle

Writer:Microhm Page View:Date:2019-02-25
The battery management system (BMS) is like the heart of a new energy vehicle, and many new energy vehicles lack the competitive power often reflected in the defects of the battery management system. For many new energy vehicle brands, it is very difficult to develop a battery management system. Because the battery management system contains many resistive components, such as precision resistors, shunts, capacitors, transistors, and so on. These products need professional brand suppliers, and technology is also critical.

At present, many automobile brand manufacturers have a series of tests for BMS, including  working voltage, single cell voltage, temperature, SOC computing function, charge and discharge control, battery thermal balance, high voltage safety function, communication and troubleshooting. However, there are many disadvantages in testing BMS with real battery pack.
Firstly. the simulation of limiting conditions may bring safety risks to the tester, such as overvoltage, overcurrent and overtemperature, which may lead to the explosion of the battery.
Secondly, the SOC estimation algorithm takes a long time to verify, and the real battery charge and discharge test takes a week or more.
Thirdly. it is difficult to simulate the specific working conditions, such as the subtle SOC difference between the manufacturing cells in the test of the equalization function, and the difference of the temperature between the manufacturing cells and the battery packs in the heat balance test of the batteries.
Fourthly, other BMS function testing, such as battery working voltage, single cell voltage, temperature, SOC calculation function, charge and discharge control, battery heat balance, high voltage safety function, equalization function, communication, fault diagnosis and resistor, face many challenges, especially in the use of precision shunt products. If the resistor is not accurate enough, it is very difficult to accurately test the battery.

In addition, the simulation of controlled object is involved in the research and development of MCU. The working principle of the motor body is mainly based on the electromagnetic induction principle. The interaction speed of the various physical quantities (such as magnetic flux, inductive electromotive force, electromagnetic force, etc.) is much faster than the change of the force and speed of the mechanical system. In order to ensure higher simulation accuracy, the simulation step size of the model is much smaller than that of the general mechanical system model.
Correspondingly, different from the general electronic control system on the automobile, the special feature of MCU is that it has high control frequency and high input signal frequency. For example, the PWM control frequency of the inverter IGBT by MCU is more than 10 kHz, and the frequency of the motor position rotation signal feedback by the motor can be more than 12kHz. This requires HIL real-time simulation system to MCU control signal acquisition and motor sensor signal simulation to achieve a very high frequency, generally requires the acquisition frequency of more than 1000 times of the signal frequency, The output frequency of the signal simulation is more than 100 times of the signal frequency.

These factors are of great significance to the research and development of battery management systems. Although many new energy vehicle manufacturers have invested a lot of money in these tests and research and development, the returns are still not up to their expectations. These fundamental reasons are that other parts technology has not reached the relevant level, especially in the testing and development of precision shunt products.

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