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Power electronic control in electrical systems 175

Fig. 5.17 A lossless snubber circuit for an inverter leg.
These new power semiconductor materials offer a number of interesting charac-
teristics, which can be summarized as follows:
. large band gap
. high carrier mobility
. high electrical and thermal conductivity.
Due to the characteristics mentioned above, this new class of power device offers a
number of positive attributes such as:
. high power capability
. operation at high frequencies
. relatively low voltage drop when conducting
. operation at high junction temperatures.
Such devices will be able to operate at temperatures up to approximately 600 C. It is

anticipated that this technology will probably offer semiconductors with character-
istics closer to the desired ones discussed in the previous section.
Another important development is associated with the matrix converter (direct
AC±AC conversion without a DC-link stage). For this converter bidirectional self-
commutated devices are needed to build the converter. At the moment research
efforts show some promising results (Heinke et al., 2000). However, a commercial
product is probably not going to be available before the next decade or so.

5.10 Conclusion

Progress in semiconductor devices achieved over the last twenty years and antici-
pated developments and improvements promise an exciting new era in power elec-