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FIGURE 5: SYSTEM COSTS IN STRING INVERTERS ARE SIGNIFICANTLY LOWER WITH SiC MOSFETS THAN WITH IGBTS. (SOURCE: INFINEON TECHNOLOGIES)
Reference designs prove the benefits
To demonstrate the benefits of using SiC MOSFETs in pho- tovoltaic (PV) string and energy storage inverters, Infineon has developed a modular reference design for 1,500-VDC systems rated up to 300 kW. The design uses the novel bidi- rectional three-level ANPC topology described above, which achieves an efficiency close to 99% in both energy flow direc- tions and which is operated at a switching frequency of up to 96 kHz (using an interleaved configuration). Power density is greater than 5 kW/kg for the complete solution, includ- ing heatsinking and all control elements, allowing 300-kW throughput in the ideal 80-kg maximum cabinet weight.
Energy usage and cost savings as a result of using SiC can be easily calculated from overall efficiency improvements. Compared with a superjunction Si MOSFET solution, for example, 1,200-V CoolSiC MOSFETs can halve the losses in an energy storage system installation and provide typically
2% extra energy and runtime. SiC MOSFETs are still more expensive than IGBTs with similar performance. But at the system level, hardware costs are reduced significantly, as high efficiency at higher switching frequencies allows the use of smaller and cheaper magnetic components and heatsinks. For example, for a 1,500-V PV string inverter, at least 5% to 10% cost savings per kilowatt can be expected (Figure 5).
Another example of a reference design demonstrating the outstanding performance of SiC in storage applications is the 11-kW bidirectional CLLC DC/DC converter with 1,200-V and 1,700-V SiC MOSFETs.5 The board is a DC/DC stage with a wide range output using a two-inductor, two-capacitor (CLLC) resonant network with bidirectional capability. This converter can operate under high-power–conversion efficiency, as the symmetric CLLC resonant network has zero-voltage– switching capability for primary power switches and synchronous-rectification commutation capability for secondary-side output rectifiers.
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REFERENCES
1D. Floricau et al. “The efficiency of three level active NPC converter for different PWM strategies.” EPE, 2009
2B. Sahan et al. “Combining the benefit of SiC T-MOSFET and Si IGBT in a novel ANPC power module for highly compact 1500-V grid-tied inverters.” PCIM Europe, 2019.
3bit.ly/3wr18A1 4bit.ly/3AI88Mk 5bit.ly/3qV3kP3
Technology Analysis What Makes SiC MOSFETs the Perfect Solution for String Inverters and Energy Storage Solutions?