As data centers, edge computing and distributed IT infrastructure continue to expand, the role of the uninterruptible power supply (UPS) has evolved beyond simply providing backup power during an outage. For critical infrastructure that requires continuous and stable operation, UPS conversion efficiency, power quality, heat generation and system flexibility during normal operation can all have an impact on overall data center performance.

In small and medium-sized data centers, edge sites and enterprise server rooms, space and cooling capacity are often more constrained. Balancing reliability with long-term energy efficiency therefore places greater importance on the power conversion technologies used within the UPS. Against this backdrop, three-level inverter technology provides an effective approach to improving UPS conversion efficiency and power quality.

From Two-Level to Three-Level: Why Topology Matters

Two-level topology represents the most traditional design for high-frequency UPS. Its topology delivers only two output voltage levels: +Vdc (positive DC-link voltage) and -Vdc (negative DC-link voltage), with the output current taking the form of square-wave approximated sine wave. Rapid switching between the two voltage levels inevitably introduces notable harmonic distortion in output waveforms. To facilitate practical deployment of this topology within UPS circuits, an additional filter system is generally installed at the output.

If add a neutral zero-level between +Vdc and -Vdc, the topology is upgraded to output three voltage levels: +Vdc/2, 0 and -Vdc/2, which is defined the three-level topology technology.

Compared with a conventional two-level topology, a three-level topology offers several key advantages:

• Lower output THD: Benefiting from an extra voltage level, three-level topology generates output voltage waveforms much similar to ideal sine waves, resulting in reduced THD and improved output power quality.

• Reduced Electromagnetic interference (EMI): Rapid voltage variation during IGBT turn-on and turn-off generates abundant high-frequency harmonics and severe EMI. Three-level topology features a lower voltage change rate (dv/dt) than two-level, which effectively cutting down EMI.

• Higher efficiency: Although three-level topology has higher conduction loss, its switching loss is substantially lower than that of two-level topology. The overall power loss of three-level topology is hence lower, enabling higher operational efficiency.

For UPS systems that operate continuously, these advantages are not isolated performance metrics. Together, they contribute to more efficient power conversion and improved overall system performance.

Why Three-Level Technology Matters for Small and Medium Power UPS Systems

As critical computing resources increasingly move into small and medium-sized data centers, server rooms and network nodes, limited deployment space and cooling capacity make UPS efficiency increasingly important.

Over continuous operation, conversion losses not only translate into additional energy consumption but are also released as heat, adding to the cooling load. Therefore: Higher UPS efficiency → Lower conversion losses → Less heat generation → Reduced cooling demand

The benefits of improving UPS conversion efficiency therefore extend beyond the UPS itself, contributing to more efficient energy use across the wider critical infrastructure environment.

Bringing Three-Level Technology to 6–200kVA UPS Systems

KSTAR applies three-level inverter technology across UPS platforms ranging from 6kVA to 200kVA, addressing different capacity and deployment requirements.

The KSTAR Memopower-IV series, covering 6–10kVA, features a single-phase input and single-phase output architecture with a three-level inverter topology. It delivers efficiency of up to 95.5% and an output power factor of 1.0.

Beyond conversion efficiency, the series supports N+X parallel redundancy with up to four units operating in parallel and provides a wide input voltage range of 110–300Vac. These capabilities enable the Memopower-IV to balance efficiency, reliability and deployment flexibility in server rooms, network infrastructure and other space-constrained critical IT environments.

For larger loads, the KSTAR YDC3300 series extends three-level inverter technology across the 50–200kVA power range.

The YDC3300 also adopts a three-level inverter topology, achieving efficiency of up to 95.5% and an input power factor of up to 0.99. Up to six units can operate in parallel, providing greater flexibility for capacity expansion and redundancy.

For more complex load environments, the YDC3300 supports 100% unbalanced loads as well as inductive and capacitive loads. Its Power Walk-in function helps reduce the impact on the upstream power system during UPS start-up, while Load Bus Synchronization (LBS) enables synchronized operation between two independent UPS systems.

Combined with three-level inverter technology, these capabilities extend the performance benefits beyond conversion efficiency alone, addressing practical data center requirements for reliability, scalability and adaptability to complex load conditions.

Powering the Future of Distributed Data Centers

Alongside large and hyperscale data centers, enterprise server rooms, edge data centers and regional IT nodes are carrying an increasing share of critical workloads. Despite differences in scale and deployment conditions, these facilities share similar requirements for critical power infrastructure: reliable power delivery, high operating efficiency, efficient use of space and the flexibility to scale.

Three-level inverter technology helps address these requirements by reducing switching losses, improving output waveforms and minimizing heat generation. For small and medium-sized data centers and distributed IT environments, these benefits translate into higher UPS efficiency, improved power quality and reduced cooling demand, supporting more efficient and reliable long-term operation.

From the 6–10kVA Memopower-IV to the 50–200kVA YDC3300, KSTAR applies three-level inverter technology across different UPS capacity ranges, combining efficient power conversion with redundancy, scalability and load adaptability. As data center infrastructure continues to evolve toward greater efficiency and more distributed architectures, three-level technology will play an increasingly important role in delivering stable, efficient and reliable power protection for critical loads.