In key infrastructure such as base stations, switches, and servers, there is pressure to ensure continuous operation and prevent power outages. Uninterruptible power supply (UPS) therefore became an uninterruptible backup AC power supply for electrical load equipment in the event of a power grid abnormality to maintain the normal operation of these electrical equipment. This article will show you how UPS works and the UPS application solutions from onsemi.
Online UPS provides better performance
Battery-powered UPSs are important in protecting sensitive equipment in data centers, medical facilities, factories, telecom hubs, healthcare, and even homes from short-term grid spikes and outages. In the event of prolonged power outages, these battery-powered UPSs can provide the short-term power necessary to pre-empt power outages and prevent data loss.
UPSs can be generally classified into “online” or “offline” UPSs. In an offline UPS, the load is connected directly to the grid. When the input power supply fails in the form of power failure or interference, the system switches to the offline UPSs battery-powered mode. The switching process generally takes about 10 milliseconds to complete, hence limiting the utility of offline UPSs in certain applications. Line interactive UPSs are another form of offline UPS that can actively regulate the voltage by boosting or decreasing the utility voltage as needed before passing it to a protected load. This way, the line interactive UPS can act as a voltage optimizer and have a longer service life because battery modes are not as often activated as offline UPSs.
Online UPSs adds DC/AC inverter circuits and battery charging and discharging circuits between the load and the power grid. Regardless of the normality of the input power supply, the inverter is always in operation, and switching delays are eliminated in online UPSs. Therefore, when an input fault occurs, the online UPS can carry out "zero interruption" switching and provide the load with emergency power supply from the battery. Similarly, the battery energy storage system (BESS) with bidirectional charger can provide continuous and seamless power supply in the event of an AC input interruption. The online UPS is the most expensive of the three, but it addresses the most power supply problems and provide the highest quality output, hence making it the best fit for high sensitivity devices, data centers, and other critical equipment.
Generally speaking, modular UPSs are more popular with designers and users and can be used to meet larger power demands by paralleling lower-power UPSs. Modular UPSs enable the rapid and simplistic expansion of existing UPS systems and helps customers profit from large-scale systems as these systems are built. However, as with any power design, the design of an efficient UPS presents challenges, and some key factors to consider include size, power regulation for both input and output, battery management, and topology.
The size of the UPS is also important, and especially so in spatially-valuable applications such as data centers. In the past, transformers have been one of the largest components in a UPS, but with the advent of more advanced semiconductor technologies, high-frequency switching circuits have replaced transformers, hence saving space. A transformer-free UPS is capable of supplying hundreds of kVA of emergency power to large data centers from standard-size cabinets.
Suitable topology and device materials are key elements of UPS hardware design
Online UPSs use pulse width modulation (PWM) to perform double conversion (AC-DC and then DC-AC), thus solving many input quality problems that offline UPSs cannot address such as low voltage overvoltage and line noise while reducing battery usage and extending battery life.
The inverter determines the UPS’s output quality and also greatly affects UPSs overall efficiency. Excellent online UPSs can output high-quality sine waves almost similar to commercial power and powering both resistive and inductive loads. These loads require the switching devices (IGBT/MOSFET) in the inverter to carry out high-frequency working mating control algorithms to minimize output noise and EMI issues arising from the switching process.
In a typical UPS, multiple stacked batteries form a complete battery pack which is managed by a battery management module for charging and discharging. To optimize battery performance and extend service life, battery pack designs must factor in load balancing, voltage and current protection, charge and discharge control, thermal management, fan control, monitoring and communication.
One of the most critical decisions in the hardware design of UPS is to select the right topology for the application to achieve a balance in both performance and cost. Although two-level topologies, such as three-phase half-bridges, have simple structures and uncomplicated control algorithms, three-level topologies (T-NPC, A-NPC, or I-NPC) can provide greater efficiency and lower loss and noise for more advanced UPSs.
Switchgear materials are equally critical, and new wide bandgap (WBG) devices, such as silicon carbide (SiC), can work with higher switching frequency and lower loss while reducing the size of passive devices, hence optimizing the overall design of the UPS.
High-quality SiC and innovative packaging processes for improved UPS performance
SiC and onsemi’s innovative packaging processes can improve density, reduce system losses and simplify cooling systems, hence helping to improve the overall system reliability for critical UPS systems that can be affected all over the body in one go. onsemi's system expertise is condensed into a series of optimized power modules which support a variety of critical power level topologies, discrete devices, and customized isolated gate drive solutions. onsemi, understanding the criticality of the UPS system, has developed a “infrastructure-class” reliability framework whose robust physical modeling provides predictable simulation results that can reflect the real state of operations, thus reducing development time.
onsemi's silicon carbide and hybrid silicon carbide modules feature packaging technologies with outstanding performance and lower thermal resistance than discrete devices, as well as easy to mount packaging to meet industry standards for leads. onsemi’s SiC modules contain SiC MOSFETs and SiC diodes, with boost modules used in the DC-DC stages of solar inverters. These boost modules use SiC MOSFETs and SiC diodes with voltage ratings of 1200 V. In addition, onsemi also has hybrid Si/SiC modules, including IGBT, silicon diodes, and SiC diodes which can be used in solar inverters, energy storage systems, and the DC-AC stages in UPS.
Offering better switching performance and higher reliability than silicon
With new technologies that delivers better switching performance and higher reliability than silicon, onsemi’s SiC diode family includes the D1, D2, and D3 series of diodes. The D1 series supports voltages of 650V, 1200V, and 1700V, is optimized for the low resistance and highest surge current rating of large-size chips, and is hence suitable for the Vienna rectifier input stage. The D2 series supports 650V voltage, and the D3 series supports 1200V voltage. Both D2 and D3 series diodes have low Vf high-speed switches and are suitable for PFC stage and output rectifier applications.
onsemi's silicon carbide MOSFET range includes the M1, M2, and M3 series, are designed to be fast and robust and offer system benefits which include high energy efficiency, reduced system size, as well cost effectiveness. The M1 series supports 1200V and 1700V voltages, are optimized for a balance of low resistance, switch loss and conduction loss of large size chips, thus making them suitable for DC-DC solid state relays, traction, motor drives, and also hard switch applications. The M2 series supports 650V and 900 V voltages, are optimized for the lowest RDS(ON) for low‑speed applications, and are hence suitable for DC-DC solid state relays, traction, and motor drives. The M3 series supports 1200V voltage, and is optimized for fast switching applications equipped with 15V-18V gate drives, hence making them suitable for hard switching applications and LLC resonant applications. For more information on the technologies and products onsemi offers for UPS applications, please refer to https://www.onsemi.com/solutions/industrial/energy-infrastructure/uninterruptible-power-supply-ups#FeaturedAssets.
Conclusion
Be it servers for cloud computing or 4G/5G base stations for mobile devices, UPSs are needed to ensure that systems are not affected by unstable power supplies, and market demand for UPSs is rapidly growing. With excellent SiC and packaging technology, onsemi’s UPS solution which is introduced in this article can meet the needs of a wide range of voltage and power UPS applications, thus making onsemi your best partner in the development of UPS products.