In recent years, with the emergence of new materials and the improvement of battery design technology, the application scope of lithium-ion battery is constantly expanded. The civil sector has expanded from the information industry (mobile phones, laptops, etc.) to energy transportation (electric vehicles, power grid peak shaving, solar energy, wind power station storage, etc.). In the field of national defense and military, lithium-ion batteries cover land, sea, air, space and many other arms.
Military lithium batteries not only need to be small and light, but also have different design requirements from civil batteries, which require that they can be used in harsh environment below 0℃ and above 50℃, and the logistics supply should be as simple as possible. As we all know, the vehicles that front-line forces can use are very limited, mainly relying on portable energy and batteries as power, so the level of energy density is also an important standard for the combat capability of front-line forces.
1. Design scheme of lithium battery for military equipment
The signal transmitting tower is mainly composed of the following parts: transmitting equipment, receiving equipment, antenna feeder system, power supply equipment and monitoring and control equipment to ensure the normal operation of communication lines and unmanned maintenance. The power supply equipment includes not only AC direct power supply driving signal tower, but also UPS backup power supply driving system to prevent power failure. Most of the early power supply used lead-acid battery as backup power supply. Due to the disadvantages of lead-acid, such as not environmental protection, low energy ratio, large volume and short service life, lithium-ion battery is gradually used as the backup power supply system of base station in new or upgraded base stations. According to the power consumption and conversion efficiency of the whole transmitting system, we calculate that the battery pack needs 48V 65ah to meet the working time requirements of customers. Due to the high voltage, large capacity and high ambient temperature of the whole battery, and in order to ensure the stability of the whole system, we use the lithium battery cell imported from Japan, which has high overall consistency. Each cell has built-in multiple protection, including explosion-proof valve, PTC, etc.
PCM protection system unit of power supply system includes: 1. Setting and detecting overcharge and over discharge protection of single string battery; 2. Temperature protection, over-current protection and short circuit protection of whole battery; 3. Balance system between single string batteries; battery power detection part includes detection system and display system. The detection adopts the current and voltage calculation method, which has very high display and detection accuracy. It can dynamically and intuitively display the battery charge and discharge state with the LCD display.
2. Design of backup power battery for mobile communication microwave transmitting tower
1) Design parameters of battery pack: the customer requires that the 1000W AC power supply system can work for two hours. According to the conversion efficiency and coordination voltage of UPS, we calculate that the voltage and capacity of the battery is 48.1v/65ah, which can meet the full load operation of the system for 150 minutes.
2) Design parameters of PCM: single section overcharge, over discharge, temperature, over current, short circuit protection, etc. The specific protection parameters are as follows:
• Single section overcharge protection voltage: 4.22 ± 0.25V
• Single section overcharge recovery voltage: 4.15 ± 0.50v
• Single section over discharge protection voltage: 3.00 ± 0.10v
• Recovery voltage of single section over discharge: 3.30 ± 0.10v
• Over current protection value of combined battery (10ms): 70A
• Charging balance current: 50 ± 10mA
• Charge balance voltage: 4.18 ± 25mV
• Battery temperature protection range (recoverable): - 20 ~ 60 ℃
• The finished battery also has short circuit protection
3) Design function of battery power monitoring system (PCM): adopt intelligent special chip, cooperate with LCD display; the display part includes: current battery capacity, current capacity percentage, current battery voltage, charging current, discharge current, remaining time of discharge, SOC and ASoC.
4) Overall structure design requirements of battery: as the base station is widely distributed and placed in the field, in addition to considering the insulation with the battery, it also needs to consider moisture-proof, not easy to aging and deterioration, so the shell structure uses fiberglass board as the main body. Due to the large number of cell combinations, we need to consider the problem of isolation and heat dissipation. We use the special engineering plastic bracket for the battery as the main body for the fixation and isolation of the lithium battery pack.
5) Secondary protection: the whole battery is equipped with abnormal over-current short-circuit protection fuse to prevent excessive current caused by abnormal battery and failure of protection board. When the PCM system is abnormal and generates excessive current, the fuse will cut off the output circuit of the whole battery pack and cannot be recovered.
6) Lithium battery cell: 18650 lithium battery cell / 18650 / 2500mah / 3.7V, imported from Japan, has good safety and consistency, so as to ensure the reliability of the whole battery pack.