5。0APPLICATION OF SIC DEVICES 5。1 Introduction When the project commenced,the team believed that,in time, SIC devices might eventually displace all silicon devices in power electronics in the broadest industrial markets。Those markets including motor drives; uninterrupted power supplies; industrial power supplies for metal coating, heating, and welding as well as large wind turbines in the power range from one kW to several 83512

megawatts。 h the U。 S。, these products are often designed for a 480 V, three-phase environment。Nora America also supplies 575 V and Europe and some other parts other world supplyindustrial three-phase power at 400 and 690 V。 This project used 690 V because it was specified

for the baseline wind turbine。At the high end of the power spectrum, some products are designed for medium voltage,

typically 2, 300 V or 4, 160 V。 Medium voltage is subject an entirely different set of safetycodes。 Me definition of medium voltage is sometimes extended to include the utility distributionsvoltage, which falls in the range of 10, 000 to 20, 000V, with 12, 500 V being the standard in the

United States。 Generation, even in the largest power plants, is often at 13, 800 V, which issometimes classified as medium voltage。 Medium voltage was not expected to be o£greatinterest in this project, but that has changed。

Some researchers have stated that SIC devices will simple cost too much to widely displace silicon devices。 This view is based on the challenge of finding solutions to the many technical problems associated with SIC and a reluctance to accept the proposition that SIC cost can ever be competitive to silicon。 A comparison today is misleading because silicon technologies have developed over a 40-year period; the resulting devices are inexpensive and almost defect free。 The author has a different , largely unsupported opinion about cost。 No product is subject to the impact of yields and economies of scale as much as the semiconductors。 Hard work and creative minds driven by competitive pressure to improve products in the electronics market, will chip away at the problems until in 20 years or so SIC power semiconductors will be cost ompetitive and dominate。

 The question in this project is whether SIC devices can be applied advantageously prior to that time, particularly the converter used in wind turbines。 To answer the question, one must expand the definition of cost competitiveness beyond just the device。The definition must also include the impact of SIC on an entire system,including the size, performance, and cost of all other system components。 Here, the unique attributes of SIC must be identified and discussed。 Theique characteristics of SIC as a wide-gap material stand out: high temperature, highvoltage (power), and high switching speed。 Each of these will be discussed next。论文网

5。2 High Temperature

High temperature electronics are increasing markedly in importance。 The total market for highower electronics is expected to be nearly $1 billion in 2008。 High temperature electronics havea leverage effect by increasing the capabilities of many larger systems。 Silicon in power devicess limited to Jess than 150 °C and manufacturers routinely limit operation to 125°C。 SOI (silicon on insulator)techniques can raise that limit for signal level devices to well above 200℃ with a potential of raising that limit to over 250℃。 However, those techniques are not feasible in high power devices。 When it comes to power semiconductors, temperature increase are at an end with silicon。

Where high temperature operation is necessary, SIC devices might be the only acceptable option for high power levels because they(not SIC MOSFETs) can operate at over 400℃。 This capability is a direct result of being a wide band-gap material。 As temperature is increased, a number of physical processes increase in intensity to interfere with the operation of a device, as intended by the designer。 These include an increase in intrinsic carries, increase in P-N junction leakage, increase in thermionic leakage, and decrease in carrier mobility。 A wide band-gap causes these processes to be less intense at any given temperature, so higher temperatures will be necessary for unacceptable levels of intensity to be reached。