Transformers for power electronics

Power electronic transformers: transformers for converters, transformers for UPS and medium frequency transformers

The experience developed by FDUEG in various fields of equipment for power electronics allows to tackle in the most effective and efficient way each situation, with products always designed upon each specific request from the customer.

The branch of power electronics bases its technology on semiconductor devices, which can be actively controlled in order to operate upon current and voltage waveforms with large freedom margins. Although products as power MOSFETs, BJTs and thyristors make up the core of power electronics converters, the typical magnetic components of the more traditional electrical technique keep on finding their usage beside them.

In particular, exploiting an electrical transformer allows to have the needed galvanic separation features, along with the deputed voltage variation for the apparatus to be fed.

Many challenges remain open in the world of power electronics. As technology progresses, the power density associated with the converters constantly increases and the switching of active components accelerates while maintaining the limits in losses and temperature increase. The magnetic apparatus, making up for the largest portion of a converter’s mass, needs to be designed keeping into account both these challenges and the typical necessities of such components.

Transformers for power electronics: transformers for converters

Particular appliances need dedicated converters, so that the power supply can be set to fit a load’s requirements. The generic converter, made up by an inverter cascaded to a rectifier, gives remarkable freedom in terms of voltage amplitude and frequency, and also in terms of power conveyed.

The total harmonic distortion factor (THD) of the DC current on the bus connecting the two converters is chosen as design parameter. A first approach to reduce the THD is increasing the number of diodes of the rectifier; this, however, implies the need to have an equal number of power lines and supplies, which in turn must be suitably phase shifted so that their waveform can feed this enhanced rectifier.

FDUEG manufactures transformers with arbitrary phase shifts on their output, fully customizable upon the needs, even on the same magnetic core to reduce the weight. Besides the most common vector group, delta-star with neutral, the company builds devices with symmetric zig-zag secondary winding (which does not induce a phase shift), or as asymmetric analogous transformers. The same phase shifts can also be attained, based upon a design choice, through the exploitation of a delta winding with appendices.

It is possible to build transformer whose voltage supply spans up to the typical 36 kV of the medium voltage transformers, in order to convey a power in the range of MVA. A low voltage secondary winding, on the other hand, can be designed to carry a current up to 3 kA.

Some low voltage converters benefit from the presence of a series inductance on the line, with the scope of making it easier to bear the switching without effects on the supply. In order to optimize materials, costs and dimensions, FDUEG proposes three-phase transformers with integrated chokes on their primary winding.

Transformers for power electronics: transformers for UPS application

An uninterruptible power supply (UPS) is a crucial component for any application that involves data management, from the simplest office to the largest data centers. Since the biggest mass memories need a constant supply to avoid data loss, it is vital to ensure the power flow is continuous, even in case of fault, line interruption or maintenance stops.

A UPS includes a group of power converters which feed the load to be secured through a battery, detecting as fast as possible the lack of the main power source to substitute it without interruption in the supply.

The transformers produced by FDUEG find their application as interface between UPS and outer system, to convey a power up to 3 MVA. They can be separated into two groups: insulation transformers for the incoming lines and converter-dedicated transformers with integrated choke as output.

Being a UPS a security measure, the transformers at its boundaries need to be totally reliable in any of their aspects. FDUEG’s transformers for UPS service are compliant to all the most stringent standards, including the norms for the medical sector: the resulting product is outstanding in quality, reliability and security.

Transformers for power electronics: medium frequency transformers

Some sectors of application, including airports or induction heating, require the usage of frequencies that are different from the usual 50 or 60 Hz commonly found in domestic or industrial environments.

Served by dedicated converters, the loads working in medium or high frequency may have the need for transformers with particular design. The need to handle relevant power has to be added to the issues involving the higher frequency; as a result, the magnetic components could be under heavy stress.

From having assisted, through the years, leading companies in the sectors making use of medium frequency, FDUEG went deep in analyzing all requirements of the transformers and reactors in use.

Besides low frequency applications, transformers are available to function with 400 Hz, or, if needed, up to 5 kHz.

The currents that can be sustained through FDUEG’s technology can reach 6 kA continuously; this can be attained by means of water cooling. The limits in temperature rise are particularly taken care of, so that the ageing of the insulation is limited. Thanks to its know-how, FDUEG approaches the market with quality and custom solutions.