10, 000 V, making its superior switching characteristics available at industrial voltages for the

first time。

Whether the improved switching speed is financially beneficial, depends on the application。 For

example, in a typical 2-quadmt drive, which comprises well over 90% of the drive market, there

is no supplemental filter whose size would be reduced by higher switching frequency。 The only

filtering is provided by the inductance of the motor。 The inductance is determined entirely by the

motor requirements and that inductance generally is adequate for current smoothing with the

switching speeds now found in drives。 Without Me need for higher speed switching, the designer

would have to look elsewhere for a reason to use SIC devices rather than the standard silicon

IGBTs。

5。 5 Wind Turbine Applications

5。 5。 1 High Voltage Aspects

The baseline turbine for this project is 1。 5 MW, but utility-scale turbines are offered up to at least3。 4 MW。 With full power conditioning in the variable-speed system the necessary converters

need to be rated the same as the turbine。 Increasing the voltage from 690 V to the medium-

voltage range makes sense at any rating over 1 MW。 That this has not happened already in the

wind industry is surprising。 Higher voltages reduce current levels inversely, along with the size

of all current carrying components-generator, wires, relays and breakers。 The most common

medium voltages in industry in North America are2, 300 V and 4, 160 V, for which many

standard components and products are available。

Medium-voltage components require more material for electrical insulation, and they must

withstand more extreme electrical events and tougher safety codes。 But the cost of these is

Generally more than offsets by the substantial reduction in material。 The tradeoff analysis associated with using medium voltage was not part of the statement of work in the project。 Also not part of the statement of work is the projection of the performance and cost of a converter

rated at medium voltage, using for example 10, 000 V SIC devices。 However, that type of

analysis is highly recommended for subsequent work。

Based on the physics of power devices in general, and SIC power devices in particular, it is

almost certain that conduction losses will be significantly reduced as the voltage is increased。

The modest reduction in conduction losses at 480 V and 690 V, as measured in this project for

SIC, would be improved considerably(perhaps to the expected result) with an increases in voltage。 With the  increases seen in the ratings of commercial utility-scale wind turbines, there is a natural inverter to increase voltage anyway, so there is a convergence of strategies。 The capability to design very compact, six-device, high speed switching inverters at medium voltage is uniquely enabled by SIC。 This is one of the most useful conclusions reached in the project。 The full impact of this conclusion will be seen later where the potential size of a medium-voltage inverter is shown。

The use of higher voltages with SIC devices leads to other possibilities。 Today, the Navy is

attempting to develop core power distribution equipment (a substation) for future ships using SIC power devices。 Navy generators would supply power at 13, 800 VAC to be distributed at 4, 160

VAC and 450VAC。 The power electronics might operate e at13, 800VAC, 4, 160VAC, or 450 VAC。When fabricated of SIC, IGBTs are expected to have stopping voltage exceeding 20 kV。 New and interesting approaches come to mind if power electronics converters can operate at up to 13,800 volt rms。 These will be discussed later。

5。5。2 High Temperature Aspects