Power Conversion & Conditioning
Power Processing Unit (PPU)
The Power Processing Unit (PPU) converts and conditions raw electrical output from heterogeneous generation sources—including AC from Stirling alternators, variable DC from solar arrays, and DC from radioisotope thermoelectric generators—into regulated DC bus power for downstream distribution. Operating at 92 percent conversion efficiency with a 100-millisecond fault ride-through, the rack-mounted assembly provides electrical isolation, maximum power point tracking, and voltage regulation within 2 percent. Lunar implementation is constrained by the vacuum environment, which restricts thermal management to conduction cooling through aluminum heat sinks, and by extreme illumination and temperature variations that drive wide input voltage swings across solar arrays alongside dynamic nuclear reactor startup transients.
Converts and conditions raw electrical output from all generation sources into regulated DC bus power
Purpose
Accept heterogeneous raw power inputs (AC from Stirling, variable DC from solar, DC from RTG) and produce clean, regulated DC bus power at standardized voltage levels for distribution via L1-PDM. Provides electrical isolation, fault protection, and power quality management.
Context
Sits between all generation sources (NUC, SOL, RTG) and the power distribution system (L1-PDM). Critical integration point where diverse sources are unified onto a common bus. Must handle source switching, load transients, and fault isolation without power interruption.
Principles
- ▸AC-DC rectification converts Stirling alternator AC output to DC
- ▸DC-DC conversion regulates variable source voltages to fixed bus voltage
- ▸Maximum Power Point Tracking (MPPT) optimizes solar array power extraction
- ▸EMI filtering prevents conducted/radiated interference between sources and loads
- ▸Galvanic isolation prevents fault propagation between sources
- ▸Voltage regulation maintains bus within tight tolerance (typically ±2-5%)
- ▸Current limiting and crowbar circuits protect against short circuits
Typical implementations
- ▸Spacecraft PPUs typically use DC-DC converters with 90%+ efficiency
- ▸ISS: 160V primary bus, 120V secondary bus, multiple converter stages
- ▸Small spacecraft: 28V unregulated or regulated bus
- ▸GaN/SiC power devices for higher efficiency and radiation tolerance
- ▸Rad-hard power MOSFETs and controllers for space applications
Lunar considerations
- ▸Wide input voltage range from solar (varies with illumination and temperature)
- ▸Must handle nuclear reactor startup transients
- ▸Radiation-hardened components required for 100-year life
- ▸Thermal management of power electronics in vacuum (conduction cooling only)
- ▸Dust protection for any exposed connectors or cooling surfaces
- ▸EMI management critical in compact installation
Specifications
Functional
| primary function | Convert and regulate power from all sources onto standardized DC bus |
| inputs | AC power from Stirling alternators (~10 kWe, variable frequency), DC power from solar arrays (~5 kWe, variable voltage), DC power from RTGs (~500 We, slowly varying voltage) |
| outputs | Regulated DC bus power (28V and/or 120V DC, TBD), Isolated auxiliary power rails for sensitive systems, Telemetry: efficiency, temperatures, fault status per channel |
| conversion efficiency pct | 92 |
| voltage regulation pct | 2 |
| input sources | 3 |
| source isolation | True |
| fault ride through ms | 100 |
| output ripple pct | 1 |
Physical
| mass kg | 80 |
| dimensions | Multiple converter modules, rack-mounted |
| materials | Rad-hard SiC/GaN power semiconductors, Ferrite core magnetics, Ceramic capacitors (COG/NPO for stability), Aluminum heat sinks, Polyimide PCB substrates |
| operating temp c | -40 to +85 (military/space grade) |
| cooling | Conduction to cold plate, no convection |
| radiation | Must tolerate >100 krad(Si) TID |
Operational
| power consumption w | 800 |
| thermal range c | -40, 85 |
| lifetime years | 30 |
| mtbf hours | 200000 |
Interfaces
Provides
- Regulated DC bus power, 10-15 kWe at standardized voltage (28V or 120V DC)
- Converter status: efficiency, temperatures, fault flags, per-channel metrics
Requires
- Raw AC power from Stirling alternators
- Raw DC power from solar arrays (variable voltage)
- Raw DC power from RTG units (slowly declining voltage)
- Source priority commands, converter enable/disable, setpoints
- Cold plate cooling for power electronics heat dissipation (~800W waste heat)
- Rack mounting structure for converter modules
- Radiation shielding for power electronics (>100 krad TID requirement)
Decomposes into
Cite this entry
Lunar Ark Codex. "Power Conversion & Conditioning" (L2-PWR-CONV). Retrieved 10 September 2026, from https://lunarark.com/entry/L2-PWR-CONV
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.