High temperature can be beneficial in two circumstances (1) if it is dictated by the application,

as it might be in electric vehicles, high performance aircraft, or down-hole drilling, or (2) if it

leads to less material and lower cost。 A wind turbine application does not require a converter

with a fundamental need for high temperature operation。 However, temperature will be important in reducing size and cost。 When higher temperature is combined with lower losses (in part due to higher voltage), the resulting inverter bridge will be perhaps one-sixth the size of a current inverter bridge, a fact that the designer should be able to translate into lower cost。 How this will be done is discussed at length later。

5。5。3 High Switching Frequency Aspects

Like high temperature,high speed switching in a wind turbine is not requirement by itself。 It is

beneficial only if it can make passive filter components smaller and less expensive。 One must

first identify what types of filter elements are necessary for a variable-speed generation system

with the full conditioning configuration。 Generally, only a single filter inductor has been used to

remove the 3 kHz PWM switching signal from the lines。 Any distortion from a single wind

wind turbines whose power is being collected at a common point。 If the wind turbine generates

alone, or power quality requirements are particularly high an L-c-L filter might be used。 

Since the second L is significant smaller than the first, and the c is not very expensive, the entire L-C-L filter array is not much more expensive than the single large filter inductor。 In any event it

is assumed here that the baseline wind turbine uses a single inductor between the converter and

the grid。 On the generator side of the converter, the current will be smoothed by the inductance

of the generator。 The baseline turbine is expected to use a PM generator, which tends to have

lower inductance than other types。 But it is still expected to have sufficient inductance without

supplementation with another inductor or without increasing the frequency。

Another potential problem on the generator side of the converter that might require passive

elements is excessive dv/dt, which is well known in the drive business as damaging to the first

several turns of the stator windings of industrial motors。 Increasing voltage would increase this

problem。 The solution is to beef up the motor (better insulation form wound stator winding,etc。)

to withstand the dv/dt beating or to insert a minimal filter to reduce dv/dt。 It is difficult to

analyze this problem because the voltage will undoubtedly be increased substantially and there is

little data available on medium-voltage motors or generators。

The bottom line is that the converter for the baseline turbine is assumed to have an inductor on

the grid side and no extra filter element on the generator side。 With minimal filter elements, the

potential cost benefit from a reduction in size due to an increase in switching frequency is

minimal。 In addition,a higher frequency itself leads to higher costs in some case because it

increases core losses and skin effect。Therefore, there are competing cost effects associated with

increased switching frequency。 The net outcome has not been determined in this project because,contrary to initial expectation the frequency probably will not be increased significantly with SIC power devices。 While switching losses are clearly lower with SIC, they are not negligible。

They can be kept low by operating at the lowest acceptable frequency, the same criterion that is

Imposed by the converter designer for silicon IGBTs。 It is not clear why that frequency would be