Transformer-Based and Transformer-Less UPSs: A Comprehensive Overview

January 29, 2024
May 2020

In the dynamic realm of Uninterruptible Power Supply (UPS) systems, two prominent technologies have emerged as leaders: Transformer-Based UPSs and Transformer-Less UPSs. Each possesses unique strengths, technical considerations, and applications, catering to diverse environments.

Transformer-Based UPSs: A Robust Legacy

For many years, Transformer-Based UPSs have set the standard. Renowned for their robustness and excellent load handling capabilities, these systems are a reliable choice, particularly for non-linear loads. Their high levels of galvanic isolation play a crucial role in shielding the load from power disturbances. However, the downside lies in their larger size and weight, attributed to the presence of transformers. Additionally, Transformer-Based UPSs tend to be less efficient than their transformer-less counterparts, impacting the overall cost of ownership.

The use of transformers in these UPSs allows for voltage step-up or step-down, ensuring the isolation of the output from the input, thereby providing added protection against power quality issues. However, the same transformers contribute to increased size, weight, and cost, along with introducing losses that diminish the overall efficiency of the system.

Refer to the figure below for a single-line diagram (SLD) depicting two paralleled online industrial UPSs with both input and output transformers regulating voltage and enhancing power quality.

Transformer-Less UPSs: Modern Efficiency

In recent years, Transformer-Less UPSs have gained traction. These systems are compact, highly efficient, and generally more cost-effective. Utilizing advanced power electronic circuits, they achieve voltage transformation and isolation without the need for bulky transformers. However, challenges arise from the lack of galvanic isolation, necessitating meticulous installation and grounding for optimal safety and performance.

Transformer-Less UPSs employ a different approach to voltage transformation, utilizing a multi-level inverter design and advanced control techniques for enhanced efficiency and reduced size. Yet, the absence of a transformer means there is no galvanic isolation between input and output, potentially exposing the load to power quality issues. Proper installation and grounding become imperative for safe operation, and these systems generally exhibit a higher power factor compared to transformer-based UPSs.

Applications: Tailoring UPSs to Environments

Transformer-Based UPSs are the preferred choice for industrial environments where load conditions are harsh and unpredictable. Their robust design and superior load handling capabilities make them ideal for demanding applications, particularly in supplying power to motor loads due to their ability to manage elevated inrush currents.

Conversely, Transformer-Less UPSs find their niche in data centers and IT applications where space and energy efficiency are paramount. With their compact design and high efficiency, they align perfectly with the needs of these settings. Furthermore, they prove suitable for noise-sensitive environments or areas with limited cooling capacity, producing less audible noise and heat compared to their transformer-based counterparts.

It is crucial to note that the decision between Transformer-Based and Transformer-Less UPSs should not be taken lightly. A thorough analysis of load requirements, installation environment, and total cost of ownership is essential for making an informed decision that aligns with specific needs.


In conclusion, both Transformer-Based and Transformer-Less UPSs contribute uniquely to the UPS landscape. By understanding their technical considerations and applications, one can make informed decisions to optimize power supply solutions.

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