Modern life is constantly breaking out and demanding a lot of data, which is stored in the data center. With the application of 5G, driverless, Internet of Things, artificial intelligence and other big data, the data center will open at an amazing speed. As we all know, the data center is a big power consumer, so it is the key point for the data center to discuss energy conservation and electricity cost saving, and the widespread application of uninterruptible power supply system (UPS) in the data center provides a congenital condition for the application of energy conservation skills. Therefore, UPS energy storage has become a hot topic of data center energy conservation in recent years. This paper presents a new concept of UPS+ energy storage joint power supply in the field of shared data center.

(1) Application and pain points of UPS power supply

①Application of UPS power supply

UPS is used to supply power for important equipment in case of power failure. When diesel generator is set in Class A data center, the backup time of UPS battery is required to be no less than 15min. Generally, lead-acid battery is used. In order to ensure the power supply quality and reliability of information equipment in the data center, UPS is necessary and has nothing to do with economic benefits.

② UPS pain points

• Because there are few power outages and few discharges in the whole battery life cycle, the battery becomes dormant property, which constitutes a waste of resources;

• UPS battery is in floating charge for a long time, and battery health is unknown;

• Generally, lead-acid batteries are used, which will be replaced in 4-5 years.

①Application of energy storage system

The energy storage system is mainly to cut the peak and fill the valley, and arbitrage the difference between peak and valley electricity prices. Energy storage system is not necessary. Without economic benefits, there is no value of equipment.

• The peak and valley electricity prices vary from place to place. The difference between peak and valley electricity prices is small in many places, and the setting of battery energy storage system can not even recover the capital money. Even in places where the difference between peak and valley electricity prices is large, the investment income of battery energy storage is not very high, so it is difficult to cause large-scale investment;

• The return period of ordinary pure energy storage projects is 7 to 8 years, and users or investors are unwilling to contribute;

BESS is mainly composed of four parts: Battery System (BS), Power Conversion System (PCS), Battery Monitoring System (BMS), and Energy Management System (EMS); At the same time, in practice, in order to facilitate planning, processing and control, the battery system, PCS and BMS are generally combined from scratch into a modular BESS, while EMS is primarily used to monitor, process and control one or more modular BESS. Figure 1 shows the architecture of BESS.

① SPS is a combination of UPS and energy storage system (UPS+BESS), which is a perfect combination of energy storage and power backup;

② The SPS concept is to select the UPS series that are suitable for frequent discharge after optimization in the newly built UPS system, and add the battery capacity of the UPS. Instead of using lead acid batteries, lead carbon batteries are used. Peak and valley electricity prices are used for charging and discharging, and part of the battery power is released every day for arbitrage. The remaining power meets the backup time requirements of the UPS;

③ Discharge to 80%~100% in case of occasional power failure, which has little impact on battery life;

④ Based on 50%+30% DOD (two charge and two discharge) of lead carbon battery, it can be recycled for 3300 days. It can be used every day for 9 years, twice the life of ordinary lead acid battery.

① After the UPS of SPS is optimized, it has UPS and PCS functions, and the cost of UPS optimization is far cheaper than that of a PCS;

② The UPS originally used two sets of lead acid batteries (for example), but now it uses four sets of lead carbon batteries. Only two sets of batteries are added, which is much less than the cost of four sets of lead carbon batteries for the energy storage system;

③ UPS generally has battery room, so it is not necessary to set up a separate container to save investment;

④ The UPS and battery rooms have been equipped with air conditioners, so no additional installation is required;

⑤ The charge for air conditioning of UPS and battery room has been included in the original cost and will not be deducted from the energy storage income.

It can be seen from this that the added contribution of SPS system (2 sets of lead carbon batteries and UPS optimization cost) is much less than that of battery energy storage system. See Table 1 for the comparison between SPS system and battery energy storage system.

① Problems with SPS

High power discharge of battery will seriously affect the life of lead acid/lead carbon battery; The capacity released by high power discharge of battery is much lower than that of lead-acid/lead carbon battery

Additional capacity of the battery.

With the addition of battery capacity, SPS charging capacity should be increased; The battery is charged and discharged repeatedly every day, which may affect the reliability of SPS.

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