I. General introduction

Uninterrupted Power Supply (UPS) is an electrical equipment continuous power without interruption, quality voltage, frequency accuracy, and stability for activities crucial as electronic devices' operation in the environmental data centers, hospitals, factories, transport, etc. A small drop in power supply will result in losses of up to a billion, maybe a loss of human life.

UPS's technology has a continuous development since the 1960s. With new material technology in semiconductors, UPS can produce high precision sine wave quality output power sources. Over the past 60 years, UPS technology has been oriented to thoroughly solve system stability issues, minimizing the average time between two failures (MTBF) to ensure the UPS system can run stably for a long time from 10 years or more.

UPS's innovation technology focuses on minimizing the total cost of ownership (TCO) by improving UPS efficiency and reducing the cost of ownership. Maintain and help the system operate "greener" to meet increasingly stringent environmental standards. TCO (*) - Total cost of ownership is a concept that allows the user to fully evaluate the cost of a system, including the initial investment cost (purchase of basic equipment and services) and expenses subsequent operating costs (including energy costs, warranty costs, interruptions costs). That why some systems will low initial investment may increase the total cost of ownership due to low efficiency, higher cost for repairing, maintenance cost requirement. In general, good quality products, despite their high initial cost, come with quality components and materials, and outstanding warranties will ensure a long time of use, reducing TCO costs in total.  

 

During 1960-1980, the semiconductor SCR technology was applied in UPS with square wave sine wave output, with very high harmonic distorted, UPS efficiency was about 85%. Until 1992, the IGBT semiconductor technology was introduced and quickly replaced the SCR semiconductor system. With IGBT technology, UPS's efficiency reached 94%.

In 2008, besides IGBT, people started to use 3-level sine wave modulation technology, combined with transformerless technology, which supported achieving efficiency up to 97% (under certain conditions). Some Japanese semiconductor manufacturers have been developing SiC semiconductor technology since the 1990s and beginning to apply it to their UPS systems. Until 2015, with the adoption of new Semiconductor technology replacing IGBT, the race for UPS efficiency reached 98.6% in normal operation mode (VFI).          

 

II. Typical UPS Topology

1. Inverter: A semiconductor module convert the AC Power source to DC Power Source.

2. Rectifier: A semiconductor module convert the DC Power source to AC Power Source

3. Battery: Battery used for Electrical Energy Storage. UPS will get the power from the battery when out of input power.

4. Charger: A small rectifier used for battery charged.

5. UPS Online Efficiency: Efficiency is calculated by percent efficiency when converting the UPS into normal operation (online). Usually, this efficiency will be calculated by the output power divided by the input power. The main shortage difference is the UPS loss (heat or spend on ancillary equipment: fans, controllers ...).

6. Online Double Conversion Mode: In this mode, UPS will provide converter electrical power in 02 levels. The first time the input power source is converted by the Rectifier module to DC, and the second time the inverter module will convert from DC to AC output. Thanks to Inverter, the UPS creates power with high-quality voltage, precise frequency, independent of the input (VFI)

7. Bypass Mode: A static bypass will straighten the output to the input power by a semiconductor module. Bypass mode provides a backup when UPS has problems with control units, Inverter, rectifier or when UPS needs maintenance or repair. There is no current switching, so the loss on the circuit board is really small. UPS efficiency can reach over 97% or even 99% in this mode. However, the quality of voltage and frequency will be affected.

 

III. UPS Efficiency Factor

1. UPS Efficiency Evaluation: There many ways to calculate UPS efficiency. One of them is calculated based on Conversion Efficiency, which will be calculated based on losses per IGBT or only calculated based on the UPS, excluding losses on other components such as capacitors, fans, etc., or divided by total inputs. Hence, the Conversion Efficiency is not the Total UPS Efficiency. Typically, a 94% conversion efficiency figure means that UPS's total efficiency will be around 90-92%. Total UPS efficiency is the number that best reflects UPS performance and is the most significant metric.

2. UPS load level: UPS efficiency varies with load level so that each UPS will have different actual efficiency. Typically, if the load is between 50-70% of the design capacity, the UPS is most efficient, and the manufacturer will usually declare this efficiency. Figures corresponding to 25%, 50%, 70%, and 100% loads will have the highest UPS performance rating. Particularly, we should focus on the load level 25-50% because UPS will usually operate at this load in standby mode.                                                                                            

 

 

UPS SiC Efficiency at differential load level

Source: www.meppi.com

3. Component Aging factor: Most critical UPS parts, such as capacitors and fans, etc., need to be replaced before their life cycle expires. As the manufacturer's recommendation, preventive maintenance is essential, helping to stabilize performance and the entire system over time. 

We must size the initial and long-term load as well as select the appropriate UPS capacity and expansion for maximum efficiency. Ideally equipped with a very high-efficiency UPS from low load to 15% for maximum expansion, UPS must have a long life and quality components with less loss over time.

 

IV.  UPS Efficiency Improvement Technology

1. Design a new energy-saving mode:

Manufacturers focus on designing UPS to add energy-saving operating modes (Eco mode, Econversion, Energy Booster, etc.) by stopping battery charging activities, running directly to utility power via bypass (ECO-mode), or running self-shutdown way of UPS modules standby so that the UPS Efficiency can increase into green efficiency lines.

In addition, some manufacturers cut off the battery completely by Switching to using supercapacitors to save electricity, using the FlyWheel, or using the integrated UPS combines Generator - DRUPS. In this way, the UPS system will not need to convert AC to DC power, which the highest efficiency.

Weakness: This method requires a qualified user to become familiar with complex operation and maintenance procedures. Some energy-saving modes will affect normal operation by reducing voltage quality to improve system efficiency.

2. Reform UPS in modular module:

Manufacturers use modular technology, in which the system UPS unit is divided into many small modules in parallel. According to reasonable load and redundancy, the UPS will operate these modules by the specific algorithm to maintain the highest UPS efficiency. This method enables UPS efficiency of up to 96%.

Weakness: This reform requires a large modular UPS chassis system from the beginning (at too low load). Due to a UPS chassis' mechanical structure, the compatibility problem of future expansion modules requires UPS manufacture to have a lot of design experience because the frame-related components are almost difficult to repair and change.

3. New waveform Topology:

UPS inverter/rectifier will be moving to applied 3 or 4-level modulation technology that makes the Rectifier and Inverter conversions less lossy. Many manufacturers choose this technology since UPS efficiency be improved overall up to over 95%.

Weakness: Only new design UPS can be applied. The old design UPS system will not be upgraded, which affect the existing customer.

Comparison Wave form IGBT 2 and 3 level Technology

Source: https://www.mitsubishicritical.com

4. Increase component efficiency

 a. IGBT module

To increase UPS efficiency, some semiconductor technology research laboratories of several Japanese manufacturers, including Mitsubishi Electric, have researched and used components with higher efficiency and longevity in Inverter and Rectifier module. Specifically, SiC technology (Silicon -Carbide structure) to replace the conventional semiconductor IGBT technology (Single Silicon structure) is used in today's UPS systems. And SiC (nano silicon ceramic) technology was one of the important material technology inventions in the 20th century. SiC has outstanding features such as high strength, lightness, super good wear resistance, and wide application in today's advanced bearing systems, heat-resistant materials.

Material structure SI Mosfet vs SIC Mosfet

Source: https://www.mitsubishicritical.com

 

Khi sử dụng vật liệu mới này trong công nghệ bán dẫn, hệ thống SiC có mức dẫn điện tổn hao chỉ bằng 1/10 so với công nghệ bán dẫn IGBT hay dùng trong UPS. Bên cạnh đó, ở chế độ “khóa”, mức năng lượng xuyên qua cao gấp 3 lần so với IGBT thông dụng, cho phép khóa triệt để và mức dòng rò rỉ cũng thấp hơn 3 lần so với các hệ IGBT thông thường. Nhờ vậy, khi SiC được sử dụng trong các linh kiện điện tử, mức tổn hao trên linh kiện có thể giảm hơn 74% so với những linh kiện IGBT có chất lượng tốt nhất.

Material structure SI Mosfet vs SIC Mosfet

Source: https://www.mitsubishicritical.com

b. Capacitor

One of the most significant improvements in UPS performance is the capacitor system. Because in the UPS structure design, capacitors play an important role in voltage frequency regulation circuits. Over time, the capacitors will age, leak, and deteriorate rapidly due to the continuous operation and affected by the UPS's internal temperature. Especially when facing high-temperature environments, the capacitor service life is only about 5-7 years. Therefore, UPS systems will need a maintenance service to replace these capacitors every 5-7 years at a high service and material cost.

With new material technologies, long-life capacitor systems have emerged that enable UPS systems to run continuously throughout their lifetime without replacement. The use of 15-year-life capacitors, long-life, high-efficiency cooling fans is the latest trend today, helping older UPS systems still improve UPS efficiency increase to 98% ( from very low load to a high load).

Comparison of TCO of UPS SiC technology from Mitsubishi Electric - Summit model with different traditional UPS systems:

Type UPS	UPS 1	UPS 2	Summit UPS
Technology	IGBT 3 Level	IGBT 2 Level	SiC IGBT
Max Efficiency	96.75%	94.10%	98.60%
Efficiency @25%load	96.07%	91.18%	98.23%
Capacitor service life	7 years	7 years	>15 years
PCB service life	10 years	10 years	>15 years
Fuse service life	7 years	7 years	7 years
Fan service life	5 years	5 years	5 years
TCO (15 years)	USD 969,814.33	USD 1,092,252.89	USD 841,678.52
Payback period compare with  UPS 1			6.5 years USD 122,635.81
Payback period compare with UPS 2			4 years USD 245,074.36

Research about TCO comparison Summit SiC UPS and some other major UPS in practical application at 25% capacity load 500KVA shows that Summit UPS can provide payback in a short time after commissioning, can save more than $ 122,635 in just 15 years (when compared with today's latest IGBT technologies).

 

 

V. Conclusion

The IEEE and the US Energy Administration have stated that in the 21st century, SiC technology will create a new revolution in the electronic industry and will save billions of dollars through this technology.

With the trend to use SiC semiconductor, the race in UPS efficiency will probably stop in the 21st century with a threshold of more than 98.6% (close to 100%), an additional savings of about 1.4% with the existing UPS system. Combined with long-life UPS components such as super durable capacitors over 15 years, these technologies can solve UPS performance problems without the need for improved control. UPS systems can last near the end of their 15 years' lifecycle while maintaining high efficiency.

    

Comparision Sic and SIC technology

Source: https://www.mitsubishicritical.com

 

ABOUT MITSUBISHI ELECTRIC:

Mitsubishi Electric has more than 50 years of experience in UPS research and manufacture (1). With the application of its latest semiconductor technology (2) into the system, Mitsubishi Electric has provided UPS that operates stably, durable, and is always ready for 24x7 projects around the globe (4 ). Mitsubishi Electric is the leader in the race for UPS efficiency (5).

(1): Since 1964

(2): All Mitsubishi Electric UPS products shall use Mitsubishi Electric's IGBTs.

(3): Availability> 99.9992% based on actual operating history.

(4): Mitsubishi Electric UPS products with a design life of up to 15 years, including AC / DC capacitors.

(5): Mitsubishi Electric's SUMMIT Series®, UPS's No. 1 on the Energy Star® page - in the AC-Double Conversion (VFI) product category.

Mitsubishi Electric – UPS Development history

Source: https://www.mitsubishicritical.com

In Vietnam, Mitsubishi Electric focuses on providing UPS solutions for data centers and super-large factories.

Typically, FPT Fornix Uptime Tier 3 Data Center was put into operation in June 2020, with a total capacity of up to 3,000 KVA. The system meets the ability to operate 24/7/365 with a design life of up to 15 years with a policy of providing redundant materials right at the site, ensuring absolute peace of mind for customers.

UPS System 3x500KVA at  FPT Fornix – Data Center, Ha Noi – Viet Nam

Source: https://www.mitsubishi-electric.vn