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15-kW Si-based 20-kW SiC-based battery charger battery charger
FIGURE 4: SiC VS. SILICON DC/DC CONVERTER DESIGN PERFORMANCE COMPARISONS
with a primary side and secondary side charges the battery. Traditionally, this would be IGBT- or Si MOSFET– based designs, with devices switching at <100 kHz and effi- ciency in the range of ~97%.
Through implementing the same converter circuit with Wolfspeed’s C3M MOSFET switching at 200–500 kHz, system- level efficiency now achieves 98.5% peak, with a dramatic improvement in overall converter size and cost (Figure 4).
If we delve into the system-level details, the most common complaint is that SiC is too expensive compared with silicon. As a power component, that could be the case; however, the performance brought to the sytem from embracing SiC will yield overall system-level cost advantages that easily out- weigh any small increase there may be in SiC component
FIGURE 5: POWER SYSTEM COST FOR A DC/DC CONVERTER (SOURCE: WOLFSPEED)
cost. Higher system efficiency, greater power density, and lower system cost all counterbalance any slight increase in device cost.
Figure 5 shows a side-by-side comparison of device switching frequency between silicon and SiC MOSFETs and the associ- ated system-level impact on the booster passive elements and cooling design. It can be clearly seen that the bulky and high-cost boost inductors, capacitors, and heatsinking can be minimized as the SiC MOSFET switching frequency increases to 60 kHz and beyond.
The actual impact of increasing switching frequency on the value and size of the boost inductor is dramatic. The boost choke size can be reduced to half that of a 16-kHz IGBT solu- tion, and costs can be reduced by approximately 40%.
Conclusion
In the renewable energy, energy storage, and energy usage markets, SiC is currently enabling a wide range of applica- tions because SiC-based solutions are proven to have higher efficiency, power density, and system cost effectiveness than traditional Si-based solutions. Designers can leverage the higher switching speeds and lower conduction losses of SiC MOSFETs to reduce the size and cost of the circuit magnetics and other passive elements to achieve dramatic power den- sity improvements without any compromise in efficiency and cost.
Guy Moxey
is senior director of power products at Wolfspeed.
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Technology Analysis Maximizing the Potential of Renewable Energy with SiC