Energy storage PCS efficiency is stuck at 98% and cannot go higher—how much change can SiC SBDs bring?
The “last mile” of PCS efficiency: where do the losses go?
In the AC/DC and DC/DC power stages of energy storage PCS, the reverse recovery loss of conventional silicon-based fast-recovery diodes is one of the key factors limiting further efficiency improvements. SiC Schottky diode (SBD) has zero reverse recovery charge (Qrr≈0), nearly eliminating diode-related losses in high-frequency switching. Measured data shows the SiC solution reduces total losses of 125kW-class PCS by 20%–30%, raising maximum system efficiency from 96%—97% to over 99%.
Energy storage converters (PCS) handle bidirectional power conversion between the battery and the grid, and their efficiency denominator is the megawatt-level power that operates year-round. A difference of a few tenths of a percentage point in efficiency translates into an annual cumulative energy difference on the order of hundreds of thousands of kWh.
In hard-switching topologies, silicon-based fast-recovery diodes (FRD) generate reverse recovery current and reverse recovery loss (Err) during turn-off, which are a non-negligible component of switching loss. The higher the switching frequency, the larger the share of this loss. Traditional silicon IGBT solutions limit the switching frequency to below 20 kHz, largely to control the rise in loss caused by diode reverse recovery.
SiC SBD's Schottky barrier structure physically eliminates the minority-carrier storage effect, so the reverse recovery charge Qrr is theoretically zero. This means that at the same switching frequency, the turn-off loss of the diode branch is greatly reduced, clearing a key obstacle for PCS to evolve toward higher frequencies and higher power density.
Specific Locations of SiC SBDs in PCS
In mainstream commercial and industrial energy storage PCS topologies, SiC SBDs mainly appear in the following locations:
- Midpoint clamping branch of the T-type three-level topology.The diode in this branch experiences reverse recovery stress in every switching cycle. The zero-Qrr characteristic of SiC SBD directly eliminates the recovery loss at this node and also reduces the turn-on loss of the associated switch (because the diode's reverse recovery current is eliminated during turn-on).
- Freewheeling and rectification paths of the bidirectional DC-DC stage.The round-trip charge/discharge efficiency of an energy storage system depends on the loss symmetry when current flows in both directions. SiC SBDs produce no reverse recovery penalty in either the charging (Buck) or discharging (Boost) direction, making the efficiency curve flatter over a wide load range.
Hypersemi's SiC SBD product line covers 650V / 1200V / 1700V voltage classes, with forward currents from 6A to over 40A. Packages include TO-247-2L, TO-247-3L, TO-220AC, TO-252, TO-263, DFN8×8, and others, directly matching the diode selection requirements for 650V buses (low-voltage side of two-level/three-level topologies) and 1200V buses (high-voltage DC side) in commercial and industrial PCS. For specific part numbers and parameters, see SiC Diode Product Page .
System-Level Benefits: More Than the Diode Itself
The high-frequency capability enabled by SiC SBDs allows the PCS switching frequency to increase from the 20 kHz range to above 50 kHz, and the size of magnetic components decreases accordingly. Smaller inductors and cooling systems mean higher power density, which directly translates into increased installable capacity under the space constraints of commercial and industrial energy storage sites. In addition, the positive temperature coefficient forward voltage drop characteristic of SiC SBDs gives them a natural current-sharing tendency when multiple devices are paralleled, reducing the thermal runaway risk of parallel designs.