Solar power

Development of a three-phase feeding converter for low power photovoltaic systems

As part of this project, the partners developed a three-phase feeding low power inverter (PAC = 1 kW) for photovoltaic systems. The advantage of three-phase feeding is that the instantaneous power remains constant over a mains period, which enables large energy stores to be eliminated, which would otherwise be necessary to offset the periodic power fluctuations in single-phase mode. 

 

Summary

To feed the DC current produced by photovoltaic systems into the mains grid, conversion to AC is necessary. This is why converters are required. The converters used in small systems with a nominal output power of PAC = 1 kW are currently mainly designed for single-phase alternating current. However, three-phase feeding has the advantage that the solar power produced can be discharged to the public mains grid split between all three mains conductors rather than symmetrically. Energy is being fed into the mains in at least two phases at all times, which significantly reduces the need for intermediate energy storage compared to a single-phase converter. 

Therefore, the project partners adopted the aim of developing a competitive three-phase converter for photovoltaic systems with a low nominal output power.

In addition to reducing module costs and extending the service life, the aim was to achieve a recyclable design by avoiding problematic materials, environmentally friendly material selection and a construction allowing easy service and dismantling.

Results:

  • It is possible to construct a three-phase PV converter with performance data that can compete with the single-phase converters currently on the market.
  • Substituting the LF (low frequency) transformer contributes to a considerable material saving.
  • The HF (high frequency) transformer used instead has a greater efficiency.
  • There is a need for optimisation in the circuit technology, as this leads to losses of efficiency.
  • Eliminating electrolyte capacitors brings about a significant increase in service life.
  • Environmentally friendly materials can be used; standard use is inhibited by a lack of acceptance among component manufacturers.
  • It is not currently possible to produce a lead free converter in Germany.

More Project Informations

Project title:  Development of a three-phase input inverter for small-scale photovoltaic modules

Project number:  0329842G

Project period:  1999 - 2001

Project region:  Germany (Berlin)

Project contact:

Herr Bosch

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Source: German National Library of Science and Technology Hannover (TIB)