In recent years, reports have shown that improvements in the performance of the semiconductors can be achieved by replacing silicon with the following:
- silicon carbide (SiC)
- semiconducting diamond
- gallium arsenide.
The first group of devices is the most promising technology (Palmour et al., 1997).
These new power semiconductor materials offer a number of interesting characteristics, 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 characteristics 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.
Fig. 5.17 A lossless snubber circuit for an inverter leg.
Progress in semiconductor devices achieved over the last twenty years and anticipated developments and improvements promise an exciting new era in power electronic systems. Snubberless operation of fully controlled semiconductors at high values of current and voltage and their rates of change will be realizable in the near future. New emerging applications of these semiconductors in areas such as Power Transmission and Distribution and High Voltage Industrial Motor Drives will be possible. The thyristor will remain the only component for certain applications, due to its unmatched characteristics. However, expected improvements of the GTO and IGBT technology and emerging new devices may replace it sooner than later. New applications and use of improved semiconductors may be possible. The next ten to twenty years will therefore see design and use of power electronic systems towards the 'silicon only' with 'no impedance' reactive power compensators and a totally electronically controlled power system as will be discussed later.
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