markets wide bandgap electronics
micro-inverters operating below 5 kW. SiC transistors will also enjoy success, and are likely to replace silicon IGBTs in 900 V or 1200 V single-phase string inverters operating above 5 kW. In 1200 V three-phase central inverters, we expect to see the introduction of SiC power modules.
Making best use of the wind Wind turbines are another form of renewables that can benefit from wide bandgap power electronics. Experiments reveal that replacing silicon IGBT-based power modules with SiC equivalents delivers an improvement in overall system efficiency of approximately 1 percent. This efficiency boost translates to an operation cost benefit of $1.50 per hour per MW for the owners of a turbine generating electricity that can be sold for $150 per MW-hour. The switch to SiC also enables a hike in power density, leading to the design of smaller power converter systems.
There are several significant barriers preventing the adoption of SiC modules: High cost, reliability concerns, and the lack of availability of products with high current ratings. Today, SiC power devices are limited to a maximum current rating of 30 A, far less than the 100-150 A rating for silicon IGBTs deployed in wind turbines.
Note that it is also unlikely that discrete SiC power semiconductors will be used in wind turbines, because one would need dozens of discretes to switch the required power. The preference will be for power modules, which integrate six or more devices in a housing for heat-sinking, possibly with protection and control circuitry included.
In virtually all cases, wind turbines are built with 1700 V power modules, which are designed to work with 690 V, three-phase mains voltages. These turbines are being built with longer and longer blades, driving up output power. This is putting pressure on the makers of power modules to increase the handling current of their products, or reduce prices. We believe that this trend is hampering the uptake of SiC modules and depressing their penetration in this application.
With wind turbines, like many other applications, device reliability is crucial. The location of the wind turbine determines the consequences of the failure of an individual module, which stops a wind turbine power converter from operating. If the turbine is on land, an electrician can make the necessary repairs in a day. But if the turbine is off-shore, specialist engineers must get on a service boat, which can only reach the required destination in good weather and never during the winter months.
Off-shore turbines tend to be larger, causing failures that lead to losses in average annual generated-electricity revenues roughly a thousand times higher than those of on-shore installations.
Aiding transportation
In traction applications three-phase 690 V mains is standard, so most power modules are typically rated at 1700 V. However, some are rated higher – the maximum is 6.5 kV. Two types of inverter tend to be used in electric traction vehicles; a main inverter for the propulsion motor drive and an auxiliary inverter for battery charging. In a two or three car tram, six power modules are needed in an inverter; ten times this are
July 2012
www.compoundsemiconductor.net 33
Industrial motor drives, such as those found on large wood-working machines, offer the greatest revenue opportunity for SiC power devices.
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