Enabling Solar and Renewable Energy Power Conversion with SiC
SiC versus Si devices in renewable energy systems
Wolfspeed is working on SiC field, with over 30 years of extensive research, and has a diverse portfolio of wide-bandgap SiC devices for all power applications that value efficiency, power density, and overall system cost.
Figure 1: Wolfspeed SiC enables solar DC/DC and DC/AC power conversion.
Hardware designers in the renewable energy sector such as solar or energy storage have capitalized on silicon carbide because of the results. SiC enables high-frequency switching without loss of efficiency; in simple terms, it means smaller circuit magnetics and flatter on-resistance (RDS(on)) over temperature, which leads to lower conduction loss at true operating conditions. Whether it is about boosting power from the PV panel or inverting power back to the grid, SiC is a clear choice, as it enables the design by increasing power density, reducing the size and weight of the system, and balancing system cost.
Wolfspeed SiC’s real design impact
At present, SiC is proving to be more efficient than traditionally used silicon. Solar string systems implement maximum power point tracking (MPPT) between a series of panels and the grid-tied inverter. The MPPT is essentially a boost converter in which efficiency and power density are critical to the performance of the system design. In past designs, the booster would be IGBT-based, with devices switching at 15–30 kHz and efficiency in the range of ~97%.
Through implementing the same booster circuit with Wolfspeed C3M MOSFET and C4D diodes, system-level efficiency now achieves 99.5% peak, with a dramatic improvement in overall MPPT size and cost (Figure 2).
Figure 2: The physical footprint of an IGBT 50-kW MPPT booster (left) in comparison with Wolfspeed’s SiC 60-kW MPPT booster (right)
The design implementation with Wolfspeed SiC is simple: Increase the switching frequency of the SiC MOSFETs and utilize the near-zero reverse-recovery characteristics of the SiC boost diodes. This helps in achieving the lowest circuit loss while minimizing the size — and hence, cost — of the boost inductors, capacitors, and cooling systems.
Why is increasing switching frequency so impactful? Because with Wolfspeed SiC devices, the system can operate at 3× to 4× the switching frequency to that of an IGBT while increasing overall efficiency.
Figure 3 shows a side-by-side comparison of device switching frequency between a silicon IGBT and a Wolfspeed SiC MOSFET and the associated 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 can be minimized as the SiC MOSFET switching frequency increases to 60 kHz and beyond.
Figure 3: SiC switching-frequency effect
It can be seen in Figure 4 the actual impact of increasing switching frequency on the value and size of the boost inductor. The boost choke size can be reduced to half of a 16-kHz IGBT solution and costs can be reduced by about 40%.
Figure 4: Boost inductor selection with IGBT and SiC MOSFET (SiC MOSFET = 47 kHz, 140 µH)
Wolfspeed SiC is currently enabling a wide range of applications 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 density improvements without any compromise in efficiency and cost.
Note: All numbers listed above are approximate and are subject to change, depending on the application.