STS – Dynamism is the Programme

In addition to the focal areas of railway and medical technology, industrial technology and aerospace, the technology of renewable energies has a strategic significance for STS.

The technology developed at STS for customized power inductive components provides manufacturers of power electronics a large number of interesting technical solutions which help implement the applicable technical requirements in the form of inexpensive and reliable products.
Extensive basic development at STS in this field has resulted in, among other things, the granting of a patent aimed specifically at an appreciable increase of efficiency.

STS produces customized power transformers and chokes from 1 to 300 kW for the power electronics of the following applications

  • photovoltaics (solar inverters, 1-phase- and 3-phase-systems for the domestic market and central inverter systems for the industrial market
  • fuel cell
  • power-heat co-generation
  • wind power

Power transformers are used to guarantee galvanic insulation and/or to facilitate a greater input range for the respective generator.

Chokes are used for the input and output filters or the step-up and step-down converter and as a sinusoidal choke in the output circuit of the power inverter.


With photovoltaics solar panels are used to convert sunlight directly into electric energy. In view of the current European funding policy, the efficiency of photovoltaic systems is a crucial factor. This is determined by the efficiency ratings of the individual elements of solar panel, power inverter and cabling including additional switching elements considered at a certain operating point.

In the solar inverter both the software (especially the MPP tracker) and the hardware determine the overall efficiency of the unit.

In transformerless solar inverter systems their efficiency is determined to a major degree by the power choke and the sinusoidal inductor.
For these applications STS develops and produces power chokes for step-up and step-down converter applications and sinusoidal chokes with negligible core losses and extremely low winding capacities. The semiconductor losses thus reduced ensure not only a particularly low DC resistance in the choke coils, but also an especially high efficiency in the unit, in particular in the part-load range.

In the case of inverter topologies with galvanic insulation a power transformer provides for the potential separation. In addition this electronic circuit variant facilitates, in interaction with a step-up converter, a wide and flexible input voltage range for the generator used.
The efficiency ratings of STS power transformers is all the better, the greater the power to be transformed. With unit power ratings of, for example, 20 kW this is up to 99.5%, and for units with 100 kW up to 99.7%.

Fuel cell:
Fuel cells generate electricity by converting hydrogen and oxygen into water in an electrochemical process. In this controlled combustion heat is also generated in the fuel cell.
The basic areas of use for fuel cells range from decentralized power and heat generation for buildings or industrial plants, the propulsion of motor vehicles, through to substitution of batteries in laptops or mobile phones.

For this application STS develops and produces power transformers and chokes for all power ranges from 1 kW up. To ensure optimum functioning of the overall system, the components can be optimized for special features, such as elevated ambient temperatures, especially compact design and especially low weight.

Further applications:
Power transformers and chokes from STS are also used in other renewable energy areas, such as power-heat co-generation and in wind power installations.
For all applications the aim in the downstream power electronics is to convert energy at reasonable cost and as efficiently as possible.


Power transformers:
STS power transformers are used for current driven resonant and hard-switching topologies. They have a high efficiency – even in the part-load range.

Chokes for step-up and step-down converters:
Depending on the generator type used, it may be necessary to provide an expanded input voltage range. In the circuit design a step-down converter can be provided for this purpose, for example.
For this application STS offers especially suitable choke solutions (e.g. litz-wire windings on ferrite core), in order to effectively process the major current ripple at high switching frequencies.

Sinusoidal chokes:
With a technology developed and patented by STS it is possible – with appropriate switching frequency – to achieve sinusoidal chokes with substantially improved electrical characteristics as compared to choke designs using iron powder pot cores:

  • up to 20 times low winding capacity
  • up to 50% low power loss of the choke in the part-load range

This means for the user an improved overall efficiency of the power inverter through

  • lower switching losses of the semiconductors
  • low power loss in the chokes

The mechanical structure of the sinusoidal choke (potted in an aluminium casing) ensures compliance with protective class IP54. The choke can therefore be mounted in the external domain. The casting resin used exhibits in addition excellent thermal conductance and is listed according to UL94-V0.



STS Expert Seminar - 9th of November 2017