High Voltage Avionics Engineering Notes

Purpose

This is the high-voltage electrical system for two electric propellant pumps. The current design sits around 210–252 V and roughly 30 kW total, with about 144 A worst-case combined DC current at the low end of the pack voltage.

The hard part is not just picking an inverter. I need a clean answer for who is allowed to energize HV, how the inverter capacitors get precharged, how the propulsion electronics power themselves, and how the system still gets forced safe if software is having a bad day.

My Responsibility

I am the Responsible Engineer for the high-voltage avionics architecture and inverter integration.

My scope covers the system electrical architecture, motor/inverter selection and interfaces, HV Control requirements, CAN command/telemetry, and coordination across the battery, BMS, precharge/main switching, sensing, and pump-drive hardware.

Architecture

The current setup uses a 60S3P propulsion battery feeding an HV BMS and HV Control path before the two motor inverters.

• Battery: 210–252 V
• Estimated total electrical load: ~30.3 kW
• Combined current at 210 V: ~144 A
• Two HBCi 100400 motor inverters
• Two LMT 30100 pump motors
• Nine distributed cell-monitor boards feeding the HV BMS
• Custom HV Control board for precharge, main switching, isolated local power, sensing, faults, and inverter CAN

The normal 8S avionics system stays electrically separate.

Inverter Sizing

The current estimates are about 16.4 kW electrical for the fuel pump and 13.9 kW for the oxidizer pump. At 210 V, that works out to roughly 78 A and 66 A.

Each HBCi 100400 has about 1.39 mF of input capacitance, so the system cannot just slam the battery onto both inverters. The precharge path has to bring that combined bus up in a controlled way before the main HV path closes.

Control and Fault Ownership

From the Flight Computer side, I want this to feel simple: request pump speed, read status, respond to faults.

The messier inverter-specific details live underneath that interface:

• the inverter handles its own motor/drive faults;
• HV Control owns local sensing, E-stop behavior, precharge, main switching, and immediate local kill behavior;
• HV BMS decides whether the pack is healthy enough to allow HV;
• Flight Computer can request a normal shutdown, but it is not the only thing capable of removing energy.

Current Status

This is still actively in design and has not been hardware-validated yet.

The architecture and major component choices are defined. The next work is the actual HV Control implementation and staged testing: source characterization, board bring-up, inverter communication, unloaded motor spin, low-power pump operation, and then gradually moving toward representative pump power.

So for now, every number on this page is either a design calculation, a component rating, or an architecture target—not a measured system result.