Why do you need a lithium battery management system?
Why do you need a lithium battery management system?
Due to its special working environment and working mode, remote instrument equipment has very high requirements for battery. It requires the battery to have a long continuous power supply capacity, and the battery life often needs to reach 1 year or even longer. Lithium battery is widely used in long-time standby remote monitoring instruments because of its many advantages, such as high working voltage, small volume, light weight, high energy density, no memory effect, no pollution, small self discharge, long cycle life and so on. Compared with Ni MH battery, lithium ion battery is 30% - 40% lighter and 60% higher in energy ratio. However, lithium batteries also have serious defects. In summary, there are the following two aspects:
(1) Security
Lithium batteries have defects such as poor safety and frequent explosion. In particular, lithium battery with lithium cobalt oxide as cathode material can not discharge with high current, and its safety is poor. In addition, over charging or over discharging of almost all kinds of lithium batteries will cause irreversible damage to the cell. Lithium battery is also extremely sensitive to temperature: if used at too high temperature, electrolyte may decompose, burn or even explode; If the temperature is too low, the performance of lithium battery will deteriorate obviously, which will affect the normal use of the equipment.
Due to the limitation of battery manufacturing process, the internal resistance and capacity of each battery unit will be different. When multiple battery cells are used in series, the charge and discharge rate of each cell will be inconsistent, which leads to the low utilization of battery capacity. In view of this, a special protection system is usually needed to monitor the health status of lithium batteries in the actual use process, so as to manage the use process of lithium batteries. Figure 1 shows the lithium battery after the electrolyte is decomposed.
(2) Maintainability
The capacity attenuation and power of lithium battery at low temperature cannot be accurately predicted, which makes the maintainability of the equipment poor. For long-term online instruments, the battery needs to be replaced regularly, while the working sites of remote monitoring equipment are scattered, and the road between each site is long, so the workload of battery replacement is huge and the cost is high. In order to reduce the maintenance workload and reduce the maintenance cost, the battery management system needs to have an accurate charge state estimation function to accurately grasp the charge state of the battery and replace the battery more purposefully; At the same time, the battery management system also needs to have low power consumption to reduce the maintenance frequency and prolong the service life of the battery. Therefore, for the long-term continuous power supply of remote monitoring instruments, the reasonable design of battery management system is of great significance to the maintenance of equipment.
However, the working characteristics of remote monitoring instruments and the inherent characteristics of lithium batteries make it very difficult to develop a battery management system to meet the requirements of such applications. There are mainly the following factors:
Firstly, in terms of the working characteristics of remote measuring instruments, in order to reduce power consumption, remote measuring instruments generally sleep and wake up periodically. Its working current changes dynamically. The working current in the wake-up stage is much higher than that in the sleep state, but the working time in the wake-up stage is much shorter than that in the sleep stage;
Secondly, the discharge curve of lithium battery is very flat, and the main power is concentrated above 3.6V voltage. Then, with the further reduction of voltage, the battery power begins to decline sharply, and the remote instrument equipment cannot send low power alarm according to the battery voltage;
Finally, the self discharge rate of lithium battery changes greatly with the fluctuation of temperature. For the instruments and equipment working in the field, the temperature conditions are very extreme, which further increases the difficulty of battery power prediction. The existing battery management system is difficult to meet these functional and performance requirements. This topic is proposed based on the above background.
