Supercapacitor DC-DC Bidirectional Converter
GaN-Based Bidirectional DC-DC Converter with Buck/Boost Mode
Rad-tolerant bidirectional DC-DC converter using GaN FETs that interfaces the wide-swinging supercap voltage (200–400 V) to the regulated main DC bus (400 V), with sub-millisecond response time for transient buffering.
Purpose
Convert between the swinging supercap voltage and the fixed bus voltage with very fast control, enabling the supercap to both inject and absorb high-current transients while maintaining bus voltage regulation.
Context
Sits between L3-ESS-SCAP-RACK and L1-PDM bus. Commanded by L3-ESS-SCAP-CTRL based on bus voltage error, supercap SOC, and load forecast. Uses Renesas ISL7023SEH or similar 100 V/200 V rad-hard GaN FET DC-DC building blocks.
Principles
- ▸Bidirectional DC-DC supports both charge (buck from bus to lower-voltage supercap) and discharge (boost from supercap to bus)
- ▸GaN FETs offer up to 10× better figure-of-merit than Si MOSFETs at high frequency; reduce package size 50% with higher efficiency
- ▸Sub-millisecond control loop bandwidth required for transient response (Li-ion BMS responds much slower)
- ▸Soft-switching topologies (LLC, dual-active-bridge) reduce switching losses at high frequency
- ▸Magnetic core size scales inversely with switching frequency — GaN enables small inductors and ferrite cores
- ▸Renesas ISL7023SEH (100 V, 60 A) and ISL70024SEH (200 V, 7.5 A) rad-hard GaN FETs targeted for 100 krad TID applications
Typical implementations
- ▸VPT rad-hard DC-DC converters with GaN technology (2024 release)
- ▸Vicor newSpace high-efficiency DC-DCs
- ▸Renesas 100 V/200 V rad-hard GaN FET solutions (using EPC die)
- ▸CPES Virginia Tech GaN-based isolated DC-DC for space
- ▸CAES 100 V bus DC-DC converters (next-generation spacecraft)
- ▸Recent rad-hard DC-DC converter for cryogenic temperatures (US Patent 10090667)
Lunar considerations
- ▸Rad-hard GaN parts already qualified to 100 krad (Si) HDR, 75 krad LDR with lot-by-lot radiation assurance (MIL-PRF-38535 Class V-like)
- ▸GaN FETs less SEE-sensitive than Si MOSFETs but require dedicated rad-hardening at die level
- ▸Wide-temperature operation (–40 to +85 °C) compatible with lunar electronics bay
- ▸Bidirectional control software updatable via authenticated DTN
- ▸Long-life electrolytic capacitors avoided — use film and ceramic only
- ▸Power density >1 kW/kg achievable with GaN technology
Specifications
Functional
| primary function | Bidirectional power conversion between supercap and main DC bus |
| inputs | Supercap rack voltage (200–400 V), Main DC bus (regulated 400 V), Control commands from L3-ESS-SCAP-CTRL |
| outputs | Regulated power flow to/from L1-PDM bus, Converter telemetry (FET temperatures, output current, efficiency) |
| input voltage range v | 200, 432 |
| output voltage v | 400 |
| rated power kw | 30 |
| peak power kw | 60 |
| switching frequency khz | 250 |
| efficiency percent peak | 97 |
| control loop bandwidth khz | 5 |
| radiation tid krad | 100 |
| topology | Bidirectional dual-active-bridge with GaN FETs |
Physical
| mass kg | 3 |
| dimensions | 250 × 200 × 80 mm |
| materials | Renesas ISL7023SEH GaN FETs (100 V, 60 A, rad-hard), Ferrite-core transformer / inductor, Film and ceramic capacitors (no electrolytic), Rad-hard PWM controller (e.g., Microchip / Microsemi), Aluminum housing with thermal interface |
| operating temperature c | -40, 85 |
| radiation tid krad | 100 |
Operational
| power consumption w idle | 5 |
| thermal range c | -40, 85 |
| lifetime years | 25 |
| mtbf hours | 250000 |
Interfaces
Provides
- Bidirectional 400 V interface, 30 kW continuous / 60 kW peak
- Converter telemetry
Requires
- Supercap bus 200–400 V
- Power setpoint commands
- Cold-plate interface (~3 kW losses)
Cite this entry
Lunar Ark Codex. "Supercapacitor DC-DC Bidirectional Converter" (L3-ESS-SCAP-DCDN). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-ESS-SCAP-DCDN
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.