ABSTRACT:
Solid-State Transformers
(SSTs) are an emergent topic in the context of the Smart Grid paradigm, where
SSTs could replace conventional passive transformers to add flexibility and
controllability, such as power routing capabilities or reactive power
compensation, to the grid. This paper presents a comparison of a 1000 kVA
three-phase, low-frequency distribution transformer (LFT) and an equally rated
SST, with respect to volume, weight, losses, and material costs, where the
corresponding data of the SST is partly based on a full-scale prototype design.
It is found that the SST’s costs are at least five times and its losses about
three times higher, its weight similar but its volume reduced to less than 80
%. In addition, an AC/DC application is also considered, where the comparison
turns out in favor of the SST-based concept, since its losses are only about half
compared to the LFT-based system, and the volume and the weight are reduced to
about one third, whereas the material costs advantage of the LFT is much less
pronounced.
KEYWORDS:
1. Induction Motor (IM)
2. Indirect Field-Oriented Control (IFOC)
3. Pulse Width Modulation
(PWM)
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. Power circuit of one converter cell used in the SST’s MV side phase
stack
EXPERIMENTAL RESULTS:
Fig.
2. MV side output voltage and resulting line current for (a) the cascaded 1000 kVA MV converter, and (b) corresponding
LV side waveforms for one of the 500 kVA LV converter units (cf. Fig. 1(b)) for
full-load active power operation.
CONCLUSION:
This paper provides a comparison of a
1000 kVA three-phase LFT and an equally rated SST with respect to material costs,
weight, volume and losses. As a direct AC/AC replacement for an LFT, the SST
solution realizes benefits with respect to volume, but on the other hand is
significantly less efficient and has at least five times higher material costs.
However, SST-based solutions can clearly outperform conventional transformers
plus LV rectifier systems in modern AC/DC applications, achieving about half
the losses and one third of the weight and volume, respectively. All in all,
SST technology has significant potential also in grid applications, especially
with the Smart Grid being heavily promoted and becoming a reality in the
foreseeable future, which increases the requirements in terms of flexibility, intelligence
and controllability. However, the usefulness of an SST can only be judged in
the context of a given application; there is not a general SST solution that
fits every need. Current state-of-the-art LFT technology evolved during more
than a hundred years, and represents therefore a truly experienced competitor.
Thus SSTs, and explicitly also their relation to various application scenarios,
regarding both, technical and economical aspects, should be prominently
included in any power electronics or energy research agenda.
REFERENCES:
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