As the core system in the UPS system of the data center, how to choose the appropriate battery type and capacity is the top priority in the work of the entire battery system. In addition, in addition to the selection of battery types and capacity calculation, there are many aspects that need to be considered in the design of the entire battery system, including battery cabinet (rack) design, battery connector and wiring design, DC switch box (cabinet) Design, etc., this paper focuses on the selection and calculation of battery type selection and capacity selection.
Type selection
Choosing a suitable battery is especially important for the uninterruptible power supply system of the data center. At present, the types of batteries that can be used in data centers are not limited to traditional lead-acid batteries. In addition to lifepo4 battery, which has attracted much attention in the battery industry, flywheels, super capacitors, hydrogen fuel cells, and flow batteries are all being used. Discuss and try to be used in data center battery systems one by one to provide more abundant and broad choices for future data center battery systems. However, at this stage, lead-acid batteries are still the mainstream choice for data center battery systems, and are the preferred battery type for most data centers; secondly, lifepo4 battery is gradually replacing lead-acid batteries in data centers in an almost irreversible situation. Status, in Europe and the United States and other countries and regions with relatively narrow regions have begun to be widely used in data center computer rooms, some countries and regions have clearly specified the use of lifepo4 battery in the design of new data centers; other battery technologies are also gradually Begin to verify the feasibility of its application in the data center, with a little large-scale application cases and experience.
Capacity calculation
As an important part of the uninterruptible power supply system, the selection design of the battery is limited by the load size and the limitation of the power supply device. Common power supply devices include UPS, HVDC, inverter, DC panel, etc. Next, the battery is used with the most common UPS. Let's take an example to illustrate the method of calculating the capacity of the battery system.
For lead-acid batteries, the selection calculation is divided into two calculation methods: constant current and constant power:
Selection according to capacity and current, referred to as constant current selection method. Generally need to know the working current, working time, termination voltage and so on. We take the 480V DC backup power system as an example. It is known that a DC backup power system with a rated voltage of 480V has an average working current of 400A. The battery pack needs to be supported for 0.5 hours during a power failure. The system is lower than the alarm voltage of 420V. The customer requires the use of 12V series Battery. The selection calculation is as follows:
① Calculate the number of batteries and the number of cells in each group: 480V÷12V=40, 40×6=240 Cells
② Calculate the termination voltage of each cell: 420V÷240 Cells=1.75Vpc
③ From this, it can be concluded that the single-cell performance requirements are constant current 400A to 1.75Vpc
④ Taking a common high-rate lead-acid battery product in a certain market as an example, by consulting the manufacturer's high-rate lead-acid battery product performance specification, the manufacturer's high-rate lead-acid battery has a maximum single power of 850W, and its product performance specification shows that, When the termination voltage of a single cell is 1.75Vpc, its 0.5-hour rate constant current discharge current value is 269A, which is less than the discharge requirement of 400A, so a single group of batteries cannot meet the performance requirements, so configure 2 groups of batteries and use them in parallel. It is 400A÷2=200A. Check the manufacturer's high-rate lead-acid battery product performance specifications again. It can be found that in the manufacturer's high-rate lead-acid battery series, the 710W type product has a single cell termination voltage of 1.75Vpc, a 0.5-hour rate constant current discharge current value of 248A, and the maximum close to the requirement.
⑤ Therefore, the selection result is: the battery system is equipped with the manufacturer's 710W high-rate lead-acid battery, each group is configured with 40, and 2 groups are connected in parallel.
According to the constant discharge power selection, referred to as the constant power selection method. Need to know the system voltage, power requirements, UPS battery side related parameters, working time and termination voltage. Let's take a 400KVA uninterruptible power supply system as an example. It is known that the UPS is a 400KVA UPS of a certain brand. Its power factor is 1, the inverter efficiency is 0.94, and the rated voltage of the DC side is 480V. The battery system needs to be supported for 0.25 hours during a power failure. The system low voltage alarm value For 400.8V, the customer requires a 12V series battery. The selection calculation is as follows:
① Calculate the total power demand of the battery system: 400KVA×1÷0.94=425.53KW
② Calculate the number of batteries and the number of cells in each group: 480V÷12V=40, 40×6=240Cells
③ Calculate the termination voltage of each cell: 400.8V÷240Cells=1.67Vpc
④ Calculate the power requirement of each individual: 425.53KW÷240Cells=1773.05W
⑤ From this, it can be concluded that the single-cell performance requirement is constant power 1773.05W to 1.67Vpc
⑥ Take a common high-rate lead-acid battery product in a certain market as an example, by consulting the manufacturer's high-rate lead-acid battery product performance specification, the manufacturer's high-rate lead-acid battery has a maximum single power of 850W, and its product performance specification. It is shown that when the termination voltage of a single cell is 1.67Vp, its 0.25-hour rate constant power discharge power value is 850W, which is less than the discharge requirement of 1773.05W, so a single group of batteries cannot meet the performance requirements, so multiple groups of batteries are configured and used in parallel. We assume that the number of battery groups is configured as 3 groups, and the current required by a single group is 1773.05 W÷3=591.02W. Check the performance specifications of the manufacturer's high-rate lead-acid battery again, and we can find that the manufacturer's high-rate lead-acid battery series, The 710W type product has a 0.25 hour rate constant power discharge power value of 710W when the single cell termination voltage is 1.67Vpc, which is the closest to the requirement.
⑦ Therefore, the selection result is: the battery system is equipped with the manufacturer's 710W high-rate lead-acid battery, each group is configured with 40, and 3 groups are connected in parallel.
For lifepo4 battery, because the system composition and design framework of lifepo4 battery of different brands are different, the constant power method is generally used for calculation, and the correctness of the configuration is verified through the charging and discharging voltage range given by the battery manufacturer. You need to know the battery side voltage range, power requirements, UPS battery side related parameters, working time, etc. when the UPS is working. We also take the 400KVA uninterruptible power supply system as an example. It is known that the UPS manlybattery brand 400KVA UPS has a power factor of 0.9, an inverter efficiency of 0.94, a DC side rated voltage of 480V, and a DC side operating voltage range of 400~620V. The battery system supports 0.25 hours. The customer requested a lithium-ion battery system. The selection calculation is as follows:
① Calculate the total power demand of the battery system: 400KVA×1÷0.94=425.53KW
② Confirm the model of the lifepo4 battery module according to the working voltage range of the DC side of the UPS. It is required that the discharge cut-off voltage of the lifepo4 battery group should not be lower than the minimum working voltage of the DC side of the UPS, and the minimum charging voltage should not be higher than the maximum working voltage of the DC side of the UPS. Taking the manlybattery high-voltage lithium-ion battery as an example, we found that the working voltage of the 512Vlifepo4 battery is 448~584V, which is in line with the 400~620V working voltage range of the UPS DC side, so we can choose the brand 512Vlifepo4 battery. The brand's 512Vlifepo4 battery includes two products, 512V50Ah and TP200 512V100Ah. The corresponding 0.25 hour rate constant power discharge power values are 93KW and 186KW, respectively. We choose TP100 512V50Ah.
③ Calculate the required number of lithium-ion battery packs: 425.53KW÷93KW=4.58, rounded up to 5 groups.
