How silicon carbide (SiC) improves efficiency, thermal performance, and reliability in online double-conversion UPS systems

SiC modules for UPS systems enhance performance in online double-conversion systems by replacing silicon components in the rectifier (AFE), inverter, and DC-DC converter stages to reduce energy losses. These stages operate continuously, so the value of SiC goes beyond the module purchase price. The better comparison is at the system level, total cost of ownership (TCO), availability, efficiency, and reliability. Compared with conventional silicon power modules, particularly IGBT-based solutions, SiC modules reduce conversion losses and generate less heat. Less heat means reduced thermal stress on power components, lower cooling and ventilation demand, and greater operating margin. This helps the UPS deliver efficient, reliable power in continuous operation.

Benefits of SiC are significant in high-power, continuously operating applications such as AI data centers, industrial facilities, and healthcare infrastructure, where power interruptions or excessive heat can affect critical loads. Smaller cooling systems, more compact power stages, and lower TCO are valuable secondary outcomes.

The high stakes in these sectors where even a millisecond of power instability can trigger a shutdown, is exactly why UPS architecture is evolving.

To understand why SiC is becoming the preferred choice, it is essential to first look at the critical role a UPS plays in preventing downtime.

Why is a UPS essential for preventing costly downtime?

For critical infrastructure targeting five-nines availability, the acceptable downtime is only 5.26 minutes per year.

In data centers, even a brief interruption can have a significant financial impact. According to Uptime Institute’s Annual outage analysis 2024 report,  16% of surveyed operators experienced a serious outage costing more than $1 million.

A reliable UPS provides the immediate power continuity needed to keep critical loads running, protect valuable equipment and data, and prevent a brief power disturbance from becoming a costly outage.

How does an online double-conversion UPS work?

While SiC devices can be used in offline, line-interactive, and online UPS systems, they deliver the greatest value in online double-conversion UPS architectures.

An online double-conversion UPS is constantly active and supplies the load through its inverter, isolating connected equipment from voltage fluctuations, frequency variations, and other utility disturbances. The power is converted in two stages:

  1. AC to DC: The rectifier or active front end (AFE) converts the incoming utility power to DC and supplies the DC link
  2. DC to AC: The inverter converts the DC-link voltage into a stable, regulated AC output for the load
UPS block diagram for online double conversion architecture

Double-conversion UPS

Where do SiC modules fit in an online double-conversion UPS?

In an online double-conversion UPS, SiC modules can be used in three active power-conversion stages:

  • AC-DC rectifier or active front end (AFE)
  • DC-AC inverter
  • Bidirectional battery DC-DC converter

The static bypass is also essential, but it typically uses thyristor-based devices because it provides an alternative power path during an overload or internal UPS fault.

In simple terms, SiC is most valuable where lower losses, higher switching frequency, or improved thermal performance create measurable system-level benefits.

2000 V silicon carbide mosfet module

Easy 2B CoolSiC™ 2000 V half-bridge module

SiC modules in the rectifier and AFE stages

The rectifier converts incoming AC into controlled DC, regulates the DC link and provides power-factor correction. It supplies the inverter and supports battery charging during normal operation.

In AFE, SiC modules reduce switching and conduction losses while supporting higher switching frequencies. Depending on the design, these characteristics can help reduce filter size, cooling demand or converter footprint.

In higher-bus-voltage UPS designs (e.g., 800 V or 1500 V DC-link), three-level SiC topologies are increasingly relevant at both the PFC and DC-DC stages because they reduce device voltage stress and can improve waveform quality. The results still depend on the circuit, voltage class, and operating conditions, but they also show where SiC can make a simpler two-level topology practical at switching frequencies where two-level silicon would produce higher losses.

In addition, the high-power factor is not exclusive to SiC. It is achieved through the rectifier topology and control strategy. SiC can help implement that functionality with lower losses and greater switching-frequency flexibility.

Inverter stage with SiC modules

The inverter converts the DC-link voltage into stable single-phase or three-phase AC. In an online UPS, it operates continuously and supplies the protected load independently of disturbances on the utility input.

Lower inverter losses can improve UPS efficiency, reduce semiconductor temperature and decrease cooling requirements. Designers can use this advantage to increase efficiency at an established switching frequency or raise the switching frequency to reduce output-filter size.

Technical benchmark: Two-level SiC vs. three-level silicon

Research indicates that a two-level CoolSiC™ inverter maintained calculated stage efficiency above approximately 99.4% from 4 kHz to 40 kHz. At 16 kHz, the calculated values were:

  • 99.56% for two-level CoolSiC™
  • 98.87% for silicon NPC2
  • 98.72% for silicon NPC1

Source:  Buschhorn, Stefan, and Klaus Vogel. "Saving money: SiC in UPS applications." PCIM Europe 2014; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management. VDE, 2014.

What is NPC?

A neutral-point-clamped (NPC) converter is a three-level topology that divides the DC-link voltage across multiple semiconductor devices. This reduces device voltage stress and improves output waveform quality, but increases circuit and control complexity compared with a two-level converter.

Note: These are inverter-stage results under the evaluated conditions, not complete UPS efficiency values.

The corresponding loss comparison estimated approximately 167 W for the two-level CoolSiC™ implementation, compared with approximately 333 W for silicon NPC2. This reduction can lower cooling effort or create thermal headroom for more output power.

Battery (buck-boost converter) DC-DC: SiC in the battery stage

The battery DC-DC converter controls power flow between the battery and DC link. It steps the voltage down during charging and up during discharging, allowing stored energy to continue supplying the inverter during an outage.

SiC is valuable in this stage when the converter requires bidirectional operation, high current, higher switching frequency or compact magnetics.

As a discrete-device reference, Infineon’s 11 kW bidirectional CLLC DC-DC design demonstrates the same operating principle using 1200 V and 1700 V CoolSiC™ MOSFETs, with peak efficiency of around 97.2%.

In higher-power UPS platforms, this bidirectional-conversion function can be implemented with CoolSiC™ MOSFET modules selected according to voltage class, module configuration, current rating, and topology.

How SiC modules reduce UPS losses and operating cost

In online UPS systems, SiC modules reduce conversion losses and cooling requirements. By generating less heat, these modules lower energy consumption, minimize thermal stress on components, and reduce the total cost of ownership (TCO) over the system's lifespan.

To see a detailed breakdown of financial savings and a technical loss comparison, read the article: How to optimize UPS system using SiC power modules. 

How to choose between full SiC, hybrid Si/SiC and IGBT modules

Full SiC is relevant when the UPS design prioritizes high efficiency, higher switching frequency, reduced cooling demand, compact filters, or higher power density. Under suitable operating conditions, it can also allow a simpler two-level topology to compete with a more complex three-level silicon implementation.

Hybrid Si/SiC can be an intermediate option. By combining silicon IGBTs with SiC diodes, hybrid modules can reduce reverse-recovery-related losses without requiring a full transition to SiC MOSFETs.

IGBT modules can still be suitable for lower-frequency, cost-sensitive UPS platforms with sufficient cooling capacity and limited space constraints. The best choice depends on operating frequency, power level, existing topology, qualification effort, and whether the system-level savings justify the module choice.

Decision rule: Evaluate SiC when lower losses can reduce energy use, cooling demand, passive-component size, cabinet space, maintenance effort, or the number of converter modules. If these benefits are limited, IGBT or hybrid Si/SiC may offer the better economic balance.

What should be considered when designing with SiC?

SiC is not a direct drop-in replacement for a slower-switching silicon stage. The design must account for:

  • Gate drive and protection
  • Power-loop and gate-loop inductance
  • Voltage overshoot and parasitic turn-on
  • Switching speed and EMI
  • Current sharing between parallel devices
  • Thermal performance and lifetime
Infineon gate driver with miller clamp and DESAT

EiceDRIVER™ 1ED3240MC12H

For example, Infineon’s EiceDRIVER™ solutions provide functions such as active Miller clamp, DESAT protection, soft turn-off, high common-mode transient immunity and two-level slew-rate control for managing SiC switching behaviour. Exact gate-voltage and protection settings must follow the selected device datasheet.

To further enhance reliability, Infineon uses .XT interconnection technology, which improves thermal resistance and cycling lifetime, essential for the 24/7 demands of healthcare and AI data center UPS systems.

Key takeaway

SiC modules deliver the most value in the continuously operating power-conversion stages of online double-conversion UPS systems: the AFE/rectifier, inverter, and bidirectional battery DC-DC converter. The design decision should be evaluated at the system level, where lower losses, less heat, reduced cooling demand, and higher efficiency can improve reliability and TCO.

See how Infineon’s complete UPS solutions can help you translate these benefits into a more efficient, reliable, and cost-effective system design.

Explore Infineon’s UPS solutions

FAQs

1. Does SiC improve UPS efficiency at partial load?

Yes. Lower switching and conduction losses can improve efficiency across a broad load range, including the partial-load conditions in which many UPS systems operate. The actual improvement depends on the topology, switching frequency, and operating conditions.

Yes. Lower power losses and heat generation can create additional thermal headroom. Depending on the design, this headroom can support higher output power from the same footprint or reduce the number of parallel converter modules required.

Start with the UPS power rating, DC-link voltage, current requirement, switching frequency, topology, and cooling conditions. Then verify the module’s voltage class, current rating, package configuration, short-circuit capability, gate-drive requirements, and thermal performance.

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