of the transformer in the Navy project is expected to be in the area of 20 kHz。 If only

transformation is required, the cost for this approach is generally higher than for a 60 Hz

transformer because a number of conversion stages are needed。 But since a complex converter

will be used anyway in the variable-speed turbine, the overall cost for solid-state conversion plus

high frequency transformation might be lower。 Galvanic isolation of the turbine from the grid

(probably required) is provided by the high frequency transformer。

All three of the unique characteristics of SIC devices are being exploited here (high-voltage, high

switching speed, and high temperature)。 The system requires a significant number of passive

filter elements, most of which are reduced in size by the high frequency of SIC devices。 As

before, high voltage and high temperature will be exploited to reduce the size of each switching

bridge。

For simplicity, this configuration is not shown with an inverter against the generator。 It could

have such an inverter, but it is assumed here that the generator is designed to tolerate an uncontrolled six pulse signal imposed by the input diode bridge and that torque regulation on the

generator shaft can be implemented through management of the current flow through the

conversion system。 This system is not bidirectional as shown。 The varying voltage from the

variable-speed generator can be regulated up or down by the duty cycle of the H-bridge。 Further

voltage regulation (down only) is available through the duty cycle of the output inverter。

It is difficult to estimate either the performance or cost of this system without further study,but it has a number of fundamental advantages,which might lead to better performance and cost compared to more conventional approaches。This approach has been enabled by SIC and could not be implemented well using silicon IGBTs。This approach could be implemented in the next two to five years。 

5。6。3 Generation At Distribution Voltage

The third configuration is not unusual except that the wind turbine generates at 13, 800 v, where

most large generators on the grid operate。 The converter can be either a two or four quadrant

design depending upon pertinent tradeoff。 Although many voltages can be found on utility

distribution systems, utilities are standardizing on 12, 500 V。 Any discrepancy between the

generation and distribution can readily be reconciled by the converter, which has an effective

variable in the form of duty cycle。

In this configuration is not transformation is needed for the wind turbine it can be connected

directly to a typical distribution system。 If the transmission voltage must be increased for

transmission to population centers, or if galvanic isolation is required, this approach would still

require transformation。

This configuration is made possible through the use of SIC IGBTs, which are expected to

eventually be capable of over 20, 000 V, which is necessary for 13, 800 VAC operation。 Losses

would be the lowest of all approaches due to the extraordinarily high voltage and the properties

of SIC IGBTs。 SIC device technology is clearly not ready for this configuration but substantial

R & D is underway。 The time frame for implementing this configuration may be 10 years。

7。 3 Packaging Concept 1 State-of-the-Art Silicon package Modified for High Temperature

7。 3。 1。 Basic Package Design

Figure 6 shows the stacks for all three concepts。 One of the current state-of-the-art approaches in

power semiconductor design uses DBC, a sandwich of copper layers around a center layer of