Foreword
In recent years, the development of global new energy and the development of battery technology have also contributed to the advancement of the auxiliary functions of battery management systems. Especially in battery protection, balance, safety, fault diagnosis, etc., has made great achievements. Domestic technology has also maintained a simultaneous high-speed development.
Among them, in the battery serial application, because of the inability to completely solve the battery consistency problem, a natural "equalization" function came into being. BMS is based on voltage-based equalization, time-based equalization, SOC-based equalization, etc. From passive equalization to active equalization, the equilibrium current grows from small to large, which seems to become the development trend of solving the problem of consistency and the “mainstream†of the capacity barrel principle. Especially in China, it seems to be the first factor to consider, the only way to go.
Equilibrium is not omnipotent, the equilibrium current is constantly amplified, and it is impossible to solve the problem in a package.
Personally believe that "equilibrium" is always a "passive" and "forced" functional technology, not omnipotent and infinite. In terms of balance, synchronization brings a lot of problems, not even safety issues (high current heat causes premature failure of PCB board, short circuit caused by component failure, safety accident caused by incomplete or incomplete redundancy design).
Where is the road? A virtuous cycle to pursue an overall improvement in battery quality
Our real way out is to do our homework on the battery and improve the battery consistency from the root and the source. Especially at the beginning of the design of the OEM system, it is necessary to fully consider the battery quality. The correct idea of ​​"battery selection at the beginning of design" is the key and direction. Can't be distorted by the current state of battery quality what we should do. Let the upstream enterprises of the battery mistakenly believe that there is a balanced function, and it can also balance large currents, and everything will be fine. It is a very serious problem. Only let us put forward the right needs, and urge the battery manufacturers to continuously improve the process and innovative technology to form a virtuous circle of development atmosphere, this is the king.
A responsibility: pass the correct demand information to the battery manufacturer
The purpose of this article is to appeal and more to be a responsibility. In fact, everyone knows the gap between domestic and foreign batteries, not the individual gap, but the gap in batch consistency. Therefore, it is more necessary to guide, pay attention to, and study. Look at the "big technology" and "technical route disputes", to pay attention to these details, to avoid paying more costs and costs in the application chain. Take a positive example: "The small cylindrical core of Panasonic, the technology is pure and green", "There is a joke that if you use two machines to measure the Panasonic battery, the curve is not the same, the first question should be your test problem." Panasonic is such a cow. In recent years, we have paid more attention to the battery capacity, how big the scale is, and how many billions of output value, but from the perspective of product quality, there is no artisan spirit.
Look at the foreign battery equalization function (personal point of view)---protective balance, stable SOC value, etc.
From a technical point of view, we look at the equilibrium state of foreign classic models, all of which are mostly “passive†and “small currentsâ€. The other party is not doing well in terms of active balancing, and the current can also be bigger, but why don't they do it? Some people say that the battery is good, then, in the "good quality battery", "can be well balanced", when choosing the choice, why did you choose the first one? From the short-term cost point of view, I will choose the second one. The other party also has an equalization function, which is not so much a "balanced battery system" as it is a "protection" to prevent overcharging or over-discharging, or other functional purposes.
(Note, the above illustration is only an example of the equalization principle)
Equilibrium status of typical foreign models:
(Data is for reference only)
| Model | Leaf | Tesla | BMW I 3 | VOLT | |
| Model s | Model 3 | ||||
| Equilibrium current (mA) | ≤200 | 100 | 100 | 100 | 100 |
1. Look at the BMS equilibrium design idea of ​​Nissan from the largest sales volume:
Analysis: Leaf equalization, if it is considered as "micro-adjusted battery capacity" is more appropriate. The current is small (the current limiting resistor should be 1/8W (feeling is larger than tesla, <200mA) is the main judgment factor. In the first state, the equalization function is turned on when the vehicle is powered on, and the capacity balance combined with the correction strategy, will the SOC be more accurate? Another state is the equilibrium state of the charging end (the data shows this function), which is balanced by pulling down the maximum voltage of the battery. The “protective balance†tastes stronger. The lithium-ion battery has the characteristics of “unpredictableâ€: parameters The correlation with the use state and environmental conditions is very strong. The voltage is unstable under the current disturbance state of the electrode, which also brings trouble to the SOC estimation.
2, Tesla balanced design
Model S
summary:
This paper is affirming the progress of balanced technology. The innovative development of equalization technology, especially from chip equalization technology, undoubtedly improves the reliability and safety of the balance. As a function of consistency compensation, it is worthy of recognition. However, from the intrinsic characteristics of the battery, it cannot be changed by the balance. Therefore, from the perspective of system integration, the improvement of battery quality and the choice of excellent battery are our fundamental direction. Don't let "beautiful balance" take our eyes and cover our eyes.
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