As a real-time monitoring, automatic equalization, intelligent charging and discharging electronic components, the battery management system (BMS) plays an important role in ensuring safety, extending life, estimating remaining power, and ensuring the normal operation of electric vehicles through a series of management and control.
According to relevant statistics, in 2013, the global battery management system market output value grew by more than 10%, and the growth rate from 2014 to 2016 will jump to 25-35%. By 2020, electric vehicles will maintain a compound annual growth rate of about 15% to 30%. In addition to the increase in the number of pure electric vehicles, plug-in hybrid vehicles and hybrid vehicles, the new 48V mild hybrid system It will also significantly promote growth. In view of this, electronic enthusiasts interviewed Li Yonglfuse's sales director in China, Cha Yong.
Li Yong, China's sales director of China, said that in order to make the battery work in a reliable and safe state, it is necessary to manage the charging and discharging state of the battery, and to supervise the safe working voltage of the battery. At present, active balancing and passive equalization are mostly used. technology.
In view of the current market, Li Yong, China's sales director of the company, said that the current demand for improving air quality based on low or zero emissions puts higher efficiency requirements on the car, as the electric load of the entire car increases (such as cars). Power boost, multimedia power, etc.) require high voltage power supply and a more powerful power supply system.
At present, there are four main types of electric vehicle/hybrid vehicle architecture: one is HEV (Hybrid), oil and electric hybrid, and the battery is charged by the engine; the second is PEV (Plug-in), oil and electricity are mixed, and the battery needs external charging; The third is BEV (Battery Electric Vehicle), which is powered by pure battery; the fourth is powered by chemical fuel cell. Cha Yong said that the current market share of oil and electric hybrid vehicles is relatively large, and will gradually transform into pure electric power in the later stage.
So, what are the advantages of lithium-ion batteries?
We know that the electric vehicle's power supply system is composed of several lithium-ion batteries.
As can be seen from the above figure, the lithium battery pack is composed of one battery unit, and each battery pack has about 500 to 7000 units, which puts higher requirements on the management and control of the battery.
Lithium battery technology will be the foundation of any type of electric vehicle. Cha Yong said that it is still improving and will provide the best cost and functionality required in the future. The cost is expected to be reduced by a quarter to one third in the next few years, and the energy density is the same. The extent of growth. In the above figure, a comparison table of lead-acid batteries, nickel-hydrogen batteries, and lithium-ion batteries shows that the advantages of lithium-ion batteries in power density and charge cycle life are irreplaceable.
What are the technical bottlenecks in lithium battery systems?
For lithium-ion battery technology, there are still many places that need further improvement. Cha Yong talks about three main points:
First, the state of charge and discharge. When the charge and discharge state is within a certain range, the battery can operate safely and reliably. High discharge and overcharge will reduce the efficiency and life of the lithium ion battery. The ideal state of charge is about 20% to 90% of the maximum charge;
Second, the safe battery operating voltage. Keep the battery voltage between a minimum of 2 V and a maximum of 4.2 V. Excessive battery voltage can cause excessive current flow. In the worst case, a short circuit can damage the battery;
Third, thermal management. Temperature control is especially important because excessive temperatures can cause an interlocking reaction during the negative electrode, which can lead to dangerous situations due to possible electrode shorts and degassing of combustible gases from organic solvents (electrolytes).
In order to make the battery work in a reliable and safe state, it is necessary to manage the charging and discharging state of the battery, and to supervise the safe working voltage of the battery. Currently, active balancing and passive equalization techniques are mostly used. Cha Yong added that for protecting device fuses, small size and high voltage are still a technical difficulty.
How to control the security?
Lithium-ion batteries need to be carefully monitored and adjusted by the battery management system. The protection of the battery management system itself ensures that this important system is safe and reliable in all situations (assembly, maintenance, normal operation).
In the case of a short circuit, it will cause a strong current on the power line. Cha Yong said that for such a situation, it is recommended to use a suitable fuse technology with a fuse with a higher breaking capacity, such as the 0HEV series of the company. Battery management systems are typically connected by high-impedance sensing lines, so short-circuit currents are significantly reduced, allowing the use of electronic fuses. Of course, the high voltage requirements depend on the battery structure.
For battery protection, Lite fuses and TVS diode protection have great advantages:
1) As a global leader in protection devices, Lite offers a full range of protection devices, including Fuse, PPTC TVS Diode, TVS Diode Array, and different protection options;
2) All devices meet AEC-Q101 and AEC-Q200 automotive certifications;
3) LAB can provide a variety of testing needs for customers.
Cha Yong pointed out that as more and more automotive applications (such as battery sensor line protection) rely on electronic fuses, and in the current electronic fuses used in cars do not define official standards, Lite has developed a standard according to AEC-Q200 guidelines. Test plan to test the suitability and reliability of the fuse in automotive applications. The test plan includes 18 tests, such as 1000 hours of high temperature and high humidity test, 1000 cycle temperature shock test, special mechanical shock and vibration test, etc. The sample size also has more stringent requirements. “It’s not enough to just do a test. How to ensure that each batch passes this test? The entire quality control system can guarantee high quality consistency and continuity. This is something that some manufacturers do not have and needs special attention.â€
In addition, Lite continues to offer more products within the qualified range of automotive application electronic fuses. For DC filter capacitors and IGBT protection, Zener diodes have been used in the past, but they do not provide the same advantages as TVS diodes, such as fast response, higher surge capability and higher reliability.
For example, car chargers communicate with other systems via the CAN bus. In dense automotive environments, CAN lines are subject to overvoltage stress caused by other transients caused by coupling or conduction of ESD or other automotive systems. In this regard, Cha Yong said that a special protection device, SM24CANA and SM24CANB, has been developed for the CAN bus. It not only has ESD capability, but also has certain anti-surge capability, and also meets AEC-Q101 automotive certification.
It is not difficult to find that the lithium battery system is composed of several single-cell batteries, the structure is relatively complicated, and it is the key to the reliable operation of the whole system. It is also highly susceptible to static electricity, switching power load, induced surge, overload, short circuit. Waiting for overcurrent and overvoltage is a threat, so it is especially important to carefully select and properly place the protection components for overvoltage and short circuit protection.
Finally, Cha Yong said that vigorous development of new energy vehicles has become the consensus of all countries. Major countries such as the United States, China, Japan, Germany, South Korea, and the United Kingdom have all established their own plans for the new energy automobile industry. The safety of new energy vehicles has always been one of the key tasks of the automotive industry. While looking forward to the rapid development of new energy vehicles, we must realize that stable, efficient, safe and reliable battery management system products are guaranteed electric vehicles. The key to normal operation is that only new energy vehicles can have a sustainable future.
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