Examining Transformer-Based together with Transformerless Uninterruptible Power Supplies
Choosing between transformer-based or transformerless uninterruptible power supplies may not be a simple ‘either/or’ decision, particularly above 10kVA. Both technologies have their devote today’s power protection scenarios but the important thing differences between them are: physical size, efficiency, noise output and the levels of input harmonic distortion which they generate.
Transformer-based Uninterruptible Power Supplies: until the early 1990s, the only design of online uninterruptible power was transformer-based. Nowadays, the look remains available but generally in larger sizes for UPS from eight to 800kVA. The most common applications because of this are large industrial sites.
The inverter generates an ac supply from its dc power source, that will be fed right into a step-up transformer. The primary function of the transformer is to increase the inverter ac voltage compared to that required by the load. The transformer also protects the inverter from load disruption, whilst also providing Galvanic isolation (a approach to isolating input and output).
Modern inverter designs use IGBTs (Insulated Gate Bipolar Transistors) in the place of more traditional switching components (such as power transistors and thyristors). CN505 power station IGBTs combine the fast-acting and high power convenience of the Bipolar Transistor with the voltage control features of a MOSFET gate to make a versatile, high frequency switching device. Therefore has given rise to stronger, efficient and reliable inverters.
Transformer-based UPS will also be furnished with a double input option as standard, which is often selected at installation simply by removing a linking connector from its input terminal. This enables it to be powered from two separate ac supply sources thus adding further resilience. A transformerless UPS can be installed with dual input capability, with supplies based on exactly the same source, but this really is typically a factory-fit option.
Transformerless Uninterruptible Power Supplies: transformerless UPS is just a newer design, commonly available from 700VA to 120kVA. The primary purpose behind the introduction of transformerless units was to reduce the overall physical size and weight thus making an uninterruptible power unit more suited to smaller installations and/or computer room/office type environments, where space might be limited. Additionally it generates much less noise and heat than its transformer-based cousin and has far lower input harmonic distortion levels rendering it appropriate for environments where electronic equipment (such as computers) may be more sensitive to this type of distortion.
In the place of the step-up transformer, a transformerless UPS runs on the staged means of voltage conversion. The initial stage combines a rectifier and booster-converter to generate a dc supply for the inverter. An uncontrolled, three-phase bridge rectifier converts the ac supply right into a dc voltage. This really is passed via a mid-point booster circuit to step the dc voltage around typically 700-800Vdc where a battery charger and inverter are powered. In the second stage, the inverter takes the supply from the booster-converter and inverts it back to an ac voltage to produce the load.
An extra advantage of this technique is that the rectifier can operate from either a three or single-phase input supply. This is configured at installation for systems around 20kVA. A get a grip on system ensures a reliable, regulated dc voltage comes to the inverter all the time and the inverter can operate irrespective of UPS output load variations or mains power fluctuations or disturbances.
Choosing between Transformer-based or Transformerless Uninterruptible Power Systems: in many applications the option between the 2 might be clear. It’s where the 2 ranges overlap, with regards to power rating, that the decision is more complicated. Consideration must be provided with then to: initial purchase cost, physical size, running costs, the installation environment, and particularly, the levels of input harmonic distortion they generate. Both designs can be operated in parallel to accomplish higher levels of availability and resilience.
Over the last decade, the gap between both of these uninterruptible power technologies has reduced as manufacturers have applied common techniques and research & development efforts to both designs. The driving force behind it’s been cost and size, alongside demands to improve operating efficiency and reduce harmonic generation. In terms of online performance, both designs provide exactly the same degree of performance and are classified as VFI systems (voltage and frequency independent – in accordance with EN/IEC 62040-3). Their principal differences are their effects on upstream supplies and the operating environment.
