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Preface

Since UPS has been taken as the most critical part in power supply and distribution system of data center, the current UPS industry is also undergoing tremendous changes. Modularized UPS has become an industry trend for increasingly mature technologies, more and more users have been or are considering using modularized UPS to build new data center. In order to cater for users’ new needs such as environment friendliness, energy conservation, high efficiency, easy expansion and maintenance, all manufactures also successively launch high-capacity Modularized UPS, the status of traditional tower-type UPS is currently being challenged.

Facing various modularized UPS in the market, a large number of UPS users are currently plagued by the questions on how to choose a suitable modularized UPS as well as differentiation of authentic modularized UPS etc. These users might as may consider INVT modularized UPS (RM Series) which will become their optimal option. This article will make detailed explanation and analysis for users.

1. Application trends of modularized UPS

In 2015, the application of modularized UPS market obtained high-speed growth amounted to 34.2%, which was much higher than growth rate amounted to 9.9% in Chinese UPS market. In the future, modularized UPS in the industry will have more widespread applications and it will be further welcomed by increasingly more users. The industry generally agrees that modularized UPS has more irreplaceable advantages than that of tower-type UPS in aspects of on-demand configuration, rapid capacity expansion, flexible installation and easy maintenance. Environment friendliness, high-efficiency, energy conservation and other aspects are mainly determined by internal circuit of UPS and the utilized technology. For example, whether it is IGBT rectification or SCR rectification, whether output has isolation transformer etc., it has little relationship with exterior structure. However, what calls for attention is that, in comparison with power-frequency machine in early period, for the reason of utilization of non-transformer design, IGBT rectification and other high-frequency technologies, currently most of modularized UPS has obvious advantages in aspects of harmonic reduction and efficiency improvement. It concurrently is technological highlight of high-frequency tower-type UPS when compared to traditional power frequency UPS.

a).With fewer devices, whether power-frequency UPS is more reliable than modularized UPS?

Power frequency UPS mainly uses silicon controlled rectifier to undertake rectification (6 pulse or 12 pulse), input power factor, harmonic current and other electrical performance indicators are relatively bad, while the circuit structure is relatively simple. After more than thirty years’ development, the technology has already become sufficiently mature. Moreover, it lies in that service life of UPS generally is relatively long, some users will habitually choose the power frequency UPS that they have used many years before for replacement. High-frequency UPS has already been launched in the market for over ten years. All manufacturers currently have become sufficiently mature in aspect of technology, the reliability of their products is almost the same when compared to power-frequency UPS in aspect of circuit structure.

As a new member of high-frequency UPS family, modularized UPS is launched slightly later. However, it has attained rapid development for its easy maintenance and other characteristics, all manufactures also competitively launch their own modularized UPS.

The modularized UPS in early period is not sufficiently mature in aspect of technology, especially some manufacturers ‘design defects in aspect of in the control logic, mode transfer, fault exit etc. have leaves the impression of low reliability of modularized UPS on partial users. As a matter of fact, after years of development, especially the application of various new devices and technologies, all mainstream manufacturers’ technologies on modularized UPS have become sufficiently mature with more reliable quality. Increasingly more high-frequency tower-type UPS products also use technology of “generic modularity” on mechanical structure so as to facilitate later-period subsequent maintenance.

It can be said that the product form is not the criteria which differentiates reliability. Product reliability is determined by manufacturers’ attitude and degree of specialization for pursuing reliability, such as whether system scheme has sufficient redundancy, whether application circuit is mature, whether device has retained sufficient margin, whether productive technology and manufacturing system are well equipped, whether exit-factory test of product is comprehensive etc.  The reliability of modularized UPS is not worse than that of power frequency machine. In the meanwhile, because of its modular structure, convenient maintenance, higher availability and more features, it become increasingly favored by the market. Thus, whether a product is reliable still hinges on manufacturer's actual strength.

INVT invests 10% of annual sales revenues for R&D and laboratory platform construction. It has successively obtained national CNAS Certificate, German TUV Certificate and United States UL Certificate. It upholds a rigorous testing attitude toward product quality reliability in R&D stage and production stage and its products are favored and well received by customers from home and abroad.

b). What’s the performance of current-sharing capability of modularized UPS?

Current sharing of modularized UPS has no essential difference with current sharing of UPS in other forms. Their performance indicators all have to observe international standards, industry standards or specifications. Referring to industry standards YDT-2165 of Ministry of Posts in China, when output power is over 4kVA, unbalanced degree of electric current of full-load output of the system is less than or equal to 5 percent. When output power is less than 4kVA, unbalanced degree of electric current of full-load output of the system is less than or equal to 10 percent.

INVT RM Series modularized UPS has good balance control capability of electric current. It has passed tests of third-party authorized certification, ultra-high indicators of its non-balanced degree of electric current with full-load state less than 1.5 percent surpass YDT-2165 testing standards of UPS industry standards.

c). Whether reliability of modularized UPS is the same with parallel-operation system of tower-type UPS?

Many users all take modularized UPS as simple parallel operation of traditional tower-type machine. However, they generally ignore the difference existing in them in aspect of operating principle. For example, if one UPS is damaged in parallel-operation system, other UPS devicesstill can normally work. Many people deem that it is the same with modularized UPS. As a matter of fact, one UPS in parallel-operation system malfunctions (switches to bypass mode), In order to avoid the short circuit incurred by different UPS output (normal mode outputs rated voltage, bypass mode outputs mains voltage), the system will integrally switch all parallel operations to bypass mode, then commercial power supply still have power-down risk, while modularized UPS doesn’t have such as risk. After one power module malfunctions, it will automatically exit from system. Residual power modules in system still can realize normal operation, consequently modularized UPS has higher utilization safety.

Figure 1: All UPS switch to bypass mode after one device in parallel-operation UPS.

d). Is modularized UPS reliable? What are common failures?

The majority of UPS failures occur at the part of power conversion (rectifying and counter-current circuit). From perspective of design concept of modularized UPS, the reliability of power conversion part is remarkably improved for utilization of power-module redundancy technology. As to other parts such as bypass, input and output power distribution, monitoring etc., due to simple circuit structure and a smaller number of devices, its own reliability is relatively high. Thus, overall usability of modularized UPS is higher than that of tower-type UPS. In terms of partial users’ feedback, malfunction conditions which easily occur in modularized UPS generally include: failed system exit incurred by power-module malfunction, failed rapid work turn-over of reserve module after malfunction of master control module, system failure incurred by inter-module communication failure, error alert incurred by various communication-line interference and failed current sharing among power modules etc.

e).Whether modularized UPS is reliable when there is no isolation transformer?

Due to restrictions of circuit topology and early-period power device, traditional power frequency UPS requires to undertake boost so as to attain the operating voltage required by load. In the meanwhile, output-end transformer also can exert influence on UPS to some extent. It equals that isolation transformer additionally forms a layer of isolation for system. In current modularized UPS, power module is generally equipped with fuse in input/output process, relay can also provide isolation for output. They exert the same significance with power frequency machine isolation transformer. In the meanwhile, once power module malfunctions, DSP can quickly make response and isolate malfunction module from the system. Thus, modularized UPS will not reduce system reliability for the reason of lacked isolation transformer. In contrast, due to large volume, heavy weight and other elements, it becomes more difficult for isolation transformer of traditional power frequency machine to be adapted to the demands of new-type data center such as high-density, high-efficiency, flexible installation etc. In the meanwhile, the loss of transformer itself also concurrently generates massive heat and shortens service life of internal devices of UPS when it reduces system efficiency.

At present, all main-stream UPS manufacturers take high-frequency UPS products which have no output isolation transformer as featured products to undertake promotion. In addition to some special scenes, the need for isolation transformer scene has become less and less.