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Hitachi has developed a SiC hybrid inverter for rail cars that is compatible with 1,500V DC overhead power supply. Hitachi employed silicon carbide (SiC) to reduce equipment size and weight, and cut power loss. SiC is attracting attention as a next-generation material to replace silicon (Si), as it is expected to lead to smaller power modules and simpler cooling systems.

Hitachi has developed a compact 3.3kV/1200A hybrid module for rail car inverters having a high voltage resistance of 3.3kV using SiC (silicon carbide), a material receiving much attention as the next generation power device material replacing Si (silicon). The hybrid module developed combines 3.3kV SiC-SBDs (Schottky barrier diode) and Si-IGBTs. To achieve a compact size module, Hitachi developed optimization technologies for the SiC-SBD structure and the Si-IGBT device characteristics taking full advantage of device, circuit and loss simulations, and succeeded in reducing the module size to approximately two-thirds that of current Si modules (Hitachi comparison). The 3.3kV compact hybrid module developed will contribute to the decrease in size, weight and power consumption of high voltage rail car inverters which draw from 1500V overhead wires.

Next Generation Inverters

In recent years, environmental measures are being undertaken on a global scale to achieve a low carbon society to preventing further global warming. There is a growing market for railways as a transport system with low environmental impact but there is also a need for compact environment-friendly rail car power modules which will contribute to decreasing the size and weight of inverters for rail cars.
Compared to the currently prominent Si, the breakdown field strength of SiC is nearly 10 times higher. The high voltage resistance allows resistance loss during conduction (ON), resulting from a thinning of the device, to be reduced thus gathering attention as a candidate material for smaller power modules or simpler cooling systems. Current domestic rail inverters are mainly designed for a high voltage of 1500V from overhead wires and therefore downsizing of high voltage power modules is important. In 2009, Hitachi developed 3kV-class SiC-SBDs which employ a JBS (Junction Barrier Schottky) structure that combines Schottky junctions with pn (positive-negative) junctions, and mounted these in a power module, which led to the development of this compact SiC hybrid module for railcar inverters.

Conventional Si Inverter   SiC Hybrid Inverter
(approx. 40% less volume)