Exjobbsförslag från företag

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Förslaget inkom 2011-08-22

sponsored project: "Pre-study: solid-state power transformer"

OBS! ANSÖKNINGSTIDEN FÖR DETTA EXJOBB HAR LÖPT UT.
The traditional power transformer is basically a mutual inductor, working at the 50Hz or 60Hz of the power grid. This low frequency results in a large required amount of iron and copper in the construction. Many sorts of disturbance in the grid are passed through to the other side of the transformer. The core is magnetised even when the transformer is not loaded, and therefore produces iron losses throughout its large volume.

A ‘solid-state’ power transformer represents a large change in the design, using a higher-frequency (and therefore much smaller) transformer, with power electronic devices on both sides to convert between the network frequency and the high frequency. This has recently become feasible at least for the lower levels in the distribution network, for providing the low-voltage (e.g. 400V) supply to customers.

Apart from potentially smaller size, the advantages of a solid-state transformer may include: better power quality on the output, providing a fairly clean waveform of a well-regulated voltage, and not passing on transients; easy combination with batteries or other dc storage, to improve long-term power quality; easier shielding of the magnetic field to keep it within the transformer unit; separation of load reactive power from the network, and provision of reactive power to the network; and possibly, with further development of components, lower overall cost even excluding the effects of better power quality. There are also disadvantages, at least when the rest of the system is unchanged: the output current is limited, so a short-circuit on the load side could drag the voltage down until the fault is stopped, rather than just blowing the nearest fuse; the ability of the transformer to maintain its output voltage over a wide range of input voltage would reduce the voltage stability of the higher-level system if many such components were used; also, with the present technology the losses and initial cost are higher.

The focus of this project can be set in more detail between the student and supervisors. Some ideas are to consider the relative merits of: different possible designs of the component itself; solid-state rather than conventional transformers in their effect on the load or the network; or adaptations needed at the load side to permit the use of solid-state transformers (for example, to solve the short-circuit problem).

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