8X Power Density Increase in SiC-Based 100kW Bidirectional DC-DC Converter

March 25, 2020 by Paul Shepard

Mitsubishi Electric Corporation has developed a new technology to integrate power devices, passives, sensors and other embedded components in the same substrate, which the company deployed in a 100kW (continuous) bidirectional dc-dc converter to achieve what is believed to be the world’s most power-dense  power converter, rated at 136kW/L, or eight times more power dense than conventional converters. The new technology is expected to contribute to the downsizing of power electronics equipment.

Mitsubishi Electric’s new integration technology enables the parasitic inductance of the switching current loop to be reduced to less than 1/10th that of conventional converters. The resulting clean switching allows high-speed commutation for high-operating frequencies in silicon carbide (SiC) MOSFETs. The technology leads to considerably smaller passive components, such as reactors for current smoothing, and capacitors, which take up much space in dc-dc converters.

Background and Details

In the effort to downsize power converters used in power electronic equipment, one of the main targets is reactors. Mitsubishi Electric’s new technology reduces the parasitic inductance of the switching current loop to less than 1nH, resulting in a high operating frequency that enables reactors to be miniaturized for higher power density.

In the case of conventional technology for power converters, the parasitic inductance of the switching current loop is large because the packaging consists of wire-bonds and passive components located outside of the case (red line in Fig. 1 below). Switching at high speed with a large parasitic inductance causes significant voltage oscillations (red waveform in Fig. 2), which can damage power devices and increases noise levels.

(click on image to enlarge)

To avoid these problems, switching speed is purposefully limited (black waveform in Fig. 2), but low-speed switching is inefficient because the loss per commutation is large (Fig. 3). Also, limited high operating frequency hinders the downsizing of reactors in power converters.

Mitsubishi Electric’s new technology allows components to be embedded in the same substrate, which reduces the parasitic inductance of the switching current loop (red line in Fig. 4) to sub-nano henry (less than 1nH) levels.

As a result, the power converter achieves switching at high speed, an inherent and desired feature of SiC devices (Fig. 5). Since the converter can be operated at high frequency (Fig. 6), passive components can be miniaturized by as much as 80%.

Future Development

Further levels of integration will be explored through the use of multi-functional components.