INVT Technology Innovation – UPS Using SiC Power Components is More Efficient and Energy Saving
Time of issue:2017-07-20
Constant development of technology has led to a gradual decrease in static UPS power loss. Earlier, online UPS with input and output transformers using thyristor technology (referred to as double conversion UPS or IEC or “VFI”) had a full load operating efficiency of only 83%-85%. At present however, full load efficiency of high frequency online interactive UPS with transistor technology (IGBT) can reach 95%-97%.
More Efficient, Less Heat
Energy efficiency in present day UPS has increased by 15%, while cooling demand has decreased, thereby increasing its reliability. Mean time between failure (MTBF) of modular UPS has increased from less than 25,000 hours to 150,000 hours. There is reduction in waveform distortion of output voltage from 5% to 1%, while noise is reduced from 95dBA to 70dBA, and area occupied is also reduced by 90%.
Even in case of double conversion UPS, efficiency has reached 96.8%, and cost per kilowatt capacity has dropped to the lowest level ever. This provides many advantages for users, however, the only way manufacturers can profit from UPS is to provide after-sales service.
These days European manufacturers are producing UPS that don’t have transformers. However, UPS without transformer is still a new concept in North America. Manufacturers like APC also use online interactive topology, although there is no frequency protection and technically it is not “online”. Even so, UPS having this kind of architecture works very well in a stable power grid.
In the 90s, Invertomatic launched an eco-mode UPS in Switzerland (ECO model, working principle displayed in Figure 1), however, its sales were not optimistic. Following this, the modular UPS introduced by industry manufacturers partially solved the load problem in most data centers. The eco-mode has a very simple working principle: if there is stable power supply, the UPS automatically switches to bypass power supply mode thereby reducing power loss, and this is a significant factor in a UPS that has been designed without a transformer. In this mode, the inverter is in standby, the UPS rectifier continues to operate and charge the battery (power required is much lower than flywheel UPS), and the bypass (thyristor switch) puts the load on the power supply. The moment there is any abnormality in power supply, the UPS’ static switch transfers the load to the inverter. A UPS operating in this mode has a significant drawback, as there is no improvement in power quality when the UPS works in bypass mode.
There are some advanced eco-mode UPS in the market presently that have much shorter switching time of 2ms instead of 4ms; there are also some UPS that can monitor distortions in load, and evaluate the power grid. However, they basically work on the same principle that there are greater energy savings when there is stable power supply.
However, this is usually risky and eco-mode suffers from the same. When there is fluctuation in power, the load switches from bypass to normal mode, which is exactly opposite to the protection provided by a double conversion UPS. There is a risk to the load whenever such switching occurs, and it is up to the user to decide how to manage the risk along with the potential benefits.
With rising electricity costs and promotion of this concept, people have accepted eco-mode. However, users don’t often consider the importance of efficiency.
UPS Using SiC Power Component is More Efficient and Energy Saving
A UPS operating in eco-mode has great advantages, however, the latest developments in silicon carbide (SiC) technology make these advantages redundant. At present, all transistors adopt traditional silicon-based components, and insulated gate bipolar transistors (IGBT) have become popular when it comes to usage in UPS.
A UPS with IGBT components has one obvious shortcoming – faster the switching speed (to achieve higher accuracy), higher the power loss. This is mainly because the upper limit of module efficiency is 96.8%, however, components using SiC can theoretically increase efficiency of double conversion UPS to 98%~99%.
Synthetic SiC powder is not something new, and it has been commercially produced for over a hundred years since 1893. Although there is the issue of high initial cost when producing IGBT using SiC, the inherent advantages in energy savings will be significant. Also, there is no transfer of critical load to the power grid, which reduces power conversion risk to a large extent.
SiC has two major advantages at the module level: smaller chip size and lower dynamic loss. At the system level, these advantages can be leveraged in a variety of ways. Low dynamic loss leads to significant increase in output power, providing an opportunity to reduce weight and reduce volume. It is worth mentioning that power can increase without additional cooling capacity, because compared with silicon-based components, the loss is reduced when using SiC, and there is higher output power under same cooling conditions. Low power loss can improve energy efficiency, making it possible to design more efficient inverters, ensuring more efficient and energy-saving UPS.
Therefore, by using SiC, the UPS no longer needs to run in eco-mode, and there is no need for online interactive UPS. When users can obtain comprehensive voltage and frequency protection with power loss of less than 1%, who needs the UPS to run in eco-mode?