INVT Technological Innovation, More Efficient and Energy-Saving for UPS Using SiC Power Device.

Time of issue:2017-08-03


Because of the technological development today, the static UPS power loss is gradually declining.Adopting the thyristor technology at an early period, the line UPS that is equipped with input/output transformers also called the dual transform UPS or VFI in IEC, which full-load operating efficiency is 83-85% only.By contrast, the full-load operating efficiency of the high-frequency line interactive UPS that adopts the IGBT technology is up to 95-97%.


More Efficient, Less Heat


While the energy efficiency of today’s UPS is improved by 15%, its cooling demand declines, thus augmenting its reliability.The mean time between failures (MTBF) of the modular UPS rises up to 150,000 hours from less than 25,000 hours, its output voltage waveform distortion declines to 1% from 5%, its noise level goes down to 70dBA from 95dBA, and its floor area is decreased by 90%.Even for the dual-transform UPS, its energy efficiency is also up to 96.8%, and the cost per kilowatt reduces to the historical lowest.When this benefits users, the unique method for UPS manufacturers to make profits is provide post-sale services.


Transformers are almost removed from the UPS made by European manufacturers, while the UPS without transformers is a new thing in North America.  Without any frequency protection, the line interactive topological structure that is used by many European manufacturers like APC is not of the line type in terms of technological perspective, however the UPS of this architecture well runs in a stable power grid.


In 1990s, the ECO UPS that was launched by Invertomatic in Switzerland has not been encouraged with optimistic sales.The modular UPS consequently launched by manufacturers in the industry was successful in overcoming some load problems facing most data centers.The ECO mode is of a simple work principle: when mains supply is stable, UPS autonomously switches to the bypass mode for power supply, lowering power loss, particularly the UPS design without transformers has the UPS rectifier working under this mode, charges the accumulator (using far less power than the flywheel UPS) while inverter is at standby, and the bypass (thyristor switch) opens to supply load power, until abnormal power happens when the UPS static switch transfers load to inverter. A salient shortcoming of the UPS running under this mode is no power quality improvement occurs when the UPS runs under the bypass mode.


Basic idea is similar for some “advanced” ECO UPS with its switchover time of 2ms instead of 4ms, some of which are capable of monitoring load distortion and making decisions concerning the power grid. Electric power can be saved under a stable power supply environment. 


But, this is often involved in risks while the ECO mode is changeless.Whenever the power bias occurs, load switches to the normal mode from the bypass mode, which is on the perfect contrary with the protection provided by the dual-transform UPS.The switch means the risk that load is exposed to, in a small amount although, offsetting users’ returns.


With the power cost rising and the new idea popularizing, the ECO mode is widely accepted, but its efficiency, an important performance indicator, is not always as high as expected.


More Efficient & Energy-Saving for UPS Using SiC


The great advantages brought about by the ECO UPS may possibly offset by the recently developed SiC technology. At present, traditional silicon controlled devices are used for transistor manufacturing; the function of the insulated gate bipolar transistor (IGBT) used for UPS manufacturing is increasingly high and reliable.


An apparent shortcoming of the UPS using IGBT is the faster the switch speed (to get high accuracy), the more the power loss.It is due to the module efficiency at the upper limit of 96.8%. When adopting SiC devices, the dual-transform UPS has its theoretical efficiency up to 98-99%.Ever since 1893 when the SiC powder was put into massive production, the manufacturing cost of IGBT made using SiC was very high at an early period, but its energy-saving effect is outstanding, and prevention of critical load from being transferred to power grid eliminates the power transfer risk.


In the system perspective, all these advantages can be utilized in many ways.Lower dynamic loss brings about significant increase of output power, poses an opportunity to reduce weight and volume.It is noteworthy that power is increasable without additional cooling capacity, because when compared to the silicon controlled devices, SiC brings in less actual loss and higher output power under the same cooling condition.Low power loss improves energy efficiency, which allows for inverters with higher efficiency, thus leading to high efficiency and energy saving when applied in UPS.


Therefore, when SiC is used, the ECO UPS can be eliminated, so can the line interactive UPS.  When users are provided with full voltage & frequency protection at the expense of less than 1% power loss, is there anybody caring for the ECO mode where UPS runs?