What technology will be used in future data center UPS?

Currently, USP is not only a power supply equipment produced to improve the reliability of IT load power supply, but also has evolved from product to system backup in order to continuously pursue reliability. Under the current architecture, further pursuit of reliability seems difficult.

In addition, the evolution from product to system is to some extent at the expense of high construction and operation costs. For data center users, it is difficult to accept the increasingly high costs. From the perspective of construction, system redundancy is the doubling of investment; from the perspective of operators, the hottest topic in data centers in recent years is "green and energy saving". In the final analysis, data center users hope to reduce the operating costs of data centers through reasonable solutions, mainly referring to electricity expenses.

The phased nature of business development inevitably leads to phased construction, and the current phased construction of UPS is far less flexible than the investment in IT equipment, and the construction pace of UPS is much larger than that of IT equipment. This will inevitably lead to waste of resources or insufficient utilization. How to make UPS construction and IT equipment expansion more compatible and adaptable is a huge bottleneck under the current UPS products and solutions.

High Voltage DC UPS

High-voltage direct current (HVDC) UPS is likely to be the next stage of UPS development, not only because HVDC UPS can reasonably inherit almost all the hot spots and cutting-edge technologies of current UPS, and not only because it can combine the strengths of traditional UPS and -48VDC communication power supply and abandon their weaknesses, but more importantly, it can better meet the reliability, economy and adaptability of load power supply on the basis of realizing all the functions of traditional UPS. However, HVDC UPS still faces a series of problems to be solved.

1. DC output voltage

For the current standard server power supply, the input voltage range is 100~240±0.1VAC, and the following brief calculation can be done.

(1) Server power supply without PFC:

The maximum voltage is 240+240×0.1=264VAC, and the peak voltage is 264×1.41=373V

The minimum voltage is 100-100×0.1=90VAC, and the valley voltage is 90×1.41=127V

(2) If the power supply has active power factor correction, its DC output is approximately 400V. The industry currently has multiple solutions for this voltage range, including 240V, 350V and 380V.

①380V solution. 28 12V battery configuration: floating charge voltage is 2.25/2V per cell, total voltage is 378V; termination voltage is 1.70/2V per cell, total voltage is 286V.

Reason: Currently, most IT equipment has PFC function, and the voltage after rectification is about 400VDC. There is no modification pressure on other components of the server power supply, and it can be considered to discharge to the minimum voltage of 286VDC.

②350V solution. 26 12V battery configuration: floating charge voltage is 2.25/2V per cell, total voltage is 351V; termination voltage is 1.70/2V per cell, total voltage is 265V.

Reason: Taking into account the power supply of IT equipment (with/without PFC), there is no pressure to modify other periods of the server power supply, etc.

③240V solution. 20 12V battery configuration: floating charge voltage is 2.25/2V per cell, total voltage is 270V; termination voltage is 1.70/2V per cell, total voltage is 204V.

Reason: It meets the current relevant safety standards within 300V, overlaps with the working voltage range of traditional electric operating power supplies, and the power distribution system is relatively mature.

2. High voltage current circuit breaker

In the power supply system, circuit breakers (air switches), insurance (fuses), and contactors (relays) are widely used. This type of circuit breaker is designed according to 220/380VAC. For large-capacity low-voltage molded case circuit breakers, it can be used in a limited DC environment. For miniature circuit breakers, it is difficult to reach an operating voltage of 250VAC and 60VDC. There are also many suppliers who can provide 125VDC/1P DC air switches, and 2P series connection can reach 250VDC. This is because the power system, DC power supply, rail transit, electric locomotives, ships, etc. require about 220VDC. However, 300-400VDC DC miniature circuit breakers are currently difficult to find, and can only be obtained by using 3P and 4P series connection. At the same time, the price of 125VDC/1P miniature circuit breakers is nearly 1 times higher than that of ordinary circuit breakers, and it is not easy to purchase on the market.

3. Security issues

The high voltage value output by the -48VDC system is lower than the safe low voltage threshold of 60VDC required by the electrical safety standard, which is relatively safe for the human body. 300VDC is a high voltage direct current, which will inevitably pose a threat to human safety. In addition to basic insulation and working insulation, protective insulation and even reinforced insulation are also required. Strict requirements will be placed on the insulation, protection and operation of the product.

4. The module has some hot-swap issues

Modular redundant design can greatly improve the reliability of the system. The basis of redundancy is that new modules can be added smoothly and modules can be removed from the system smoothly and promptly when they fail. The hot swap of modules faces the same arcing problem as circuit breakers due to the presence of DC high voltage.

5. Lack of standards

In the EU communication standard "ETSI EN 3001 323 V1.2.1" (2003-08), environmental engineering: power interface at the input end of communication equipment; Part 3: "rectified power supply, AC power supply, up to 400V DC power supply", there are relatively comprehensive regulations on the scope, definition, interface, voltage range, overvoltage and overcurrent protection, grounding, safety requirements, EMC, etc. of this type of power supply. However, authoritative organizations such as IEC and national standards have not yet made provisions for high-voltage DC UPS that are generally followed by the industry.

6. Industry integration

In fact, there are solutions to the technical problems faced by the above-mentioned high-voltage DC UPS. The biggest problem lies in the integration of the industrial chain. Since the evolution of high-voltage DC UPS involves not only the UPS industry, but also the low-voltage power distribution industry, server industry and other industries, the interests of all parties are not consistent, and it also takes time to integrate.