INVERTER I TECHNOLOGY
that have the shortest possible recovery time. In many cases these FRDs are integrated within the power module.
Next-Generation IEGT/SiC power module To further enhance the effi ciency of high-power IEGT modules, Toshiba has introduced its latest-generation IEGT modules with integrated Silicon carbide (SiC) Schottky Barrier Diodes (SBDs). Figure 1 shows the connections and internal circuit of the module. As a wide bandgap semiconductor technology, SiC allows greater effi ciency and reliability than conventional silicon devices such as fast-recovery diodes. So far, a relatively small number of manufacturers, including Toshiba, have successfully brought SiC products to market. SiC SBDs are effective replacements for silicon diodes for power conversion and
been shown to have saturation voltage of less than 3.0V when conducting 1200A at an applied voltage of 850V. It can turn off a high current quickly and has low switching losses, since the turn-off energy (Eoff) can be as much as 30% less than that of a conventional device. In addition, the module provides guaranteed operation up to 150°C. The co-packaged SiC SBD has forward current rating of 600A with low forward voltage of 2.8V, and is highly suited to traction inverter applications. The leakage current of the SiC SBD is less than 10µA.
With its improved reverse-recovery characteristic the SiC SBD effectively reduces both turn-on loss and reverse-recovery loss. In fact, the reverse recovery loss is less than one tenth of the loss when using a conventional silicon diode. Figures 2a and
With its improved reverse-recovery characteristic the SiC SBD
effectively reduces both turn-on loss and reverse-recovery loss. In fact, the reverse recovery loss is less than one tenth of the loss when using a conventional silicon diode
switching across a wide range of power ratings and commercial applications. They can offer up to 50% greater effi ciency than conventional silicon diodes, and also offer improved stability up to high voltages and currents owing to reduced heat generation.
Solar thermal management Offering a valuable increase in effi ciency as well as thermal management, SiC technology is desirable in applications such as solar inverters. High-power string inverters are currently the most attractive target for SiC diodes and transistors, while cost-sensitive microinverters are expected to combine silicon transistors with SiC diodes.
Toshiba’s latest hybrid module combines 1700V/1200A silicon IEGTs in a half-bridge connection, with anti-parallel SiC SBDs, in the 130mm x 140mm x 38mm module size. The IEGT has
2b illustrate the infl uence of the SiC diode in reducing module reverse-recovery losses and turn-on losses. The lower waveforms shown in fi gure 2a illustrate the signifi cant reduction of reverse- recovery current leading to the 97% saving in reverse-recovery energy losses illustrated in fi gure 2b. The upper waveform of fi gure 2a shows how using a SiC SBD also yields a valuable saving in turn-on energy.
The plastic module package is designed to provide high reliability and low thermal resistance. Internally the module features an aluminium silicon-carbide (Al-SiC) Metal Matrix Composite (MMC) baseplate material, which has extremely low thermal resistance and a low Coeffi cient of Thermal Expansion (CTE) allowing the internal structure to be optimised for excellent lifetime characteristics with low thermal fatigue and the ability to withstand a high number of thermal cycles. The construction of the module features materials displaying high Comparative Tracking Index (CTI), and allows a high insulation-withstand voltage.
Module performance analysis Figure 3 compares the loss performance of a half-bridge inverter using the latest 1700V/1200A hybrid IEGT/SiC-SBD module and a previous-generation device featuring conventional silicon Fast-Recovery Diodes (FRDs). The diagram shows that the total hybrid module energy loss is as much as 30% lower than the losses of the earlier module.
The signifi cant improvement in effi ciency delivers further advantages by allowing the size of any cooling systems and other motor-control components to be reduced. Overall, this can allow the size of the inverter to be reduced by as much as 40%.
Figure 3. The hybrid IEGT/SiC-SBD module has lower energy losses compared to the previous generation.
©2014 Permission required. Angel Business Communications Ltd.
Issue IV 2014 I
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