Primary Electrical Power System (EPS) – Space Station OS

Overview

The Electrical Power System (EPS) is responsible for collecting, managing, and distributing power across the space station. It mimics the real ISS power architecture, including solar tracking, battery charge/discharge regulation, fault protection, and dynamic routing of power to downstream systems.

The primary components implemented include:

• SARJ (Solar Alpha Rotary Joint)
• Battery Manager
• BCDU (Battery Charge/Discharge Unit)
• MBSU (Main Bus Switching Unit)
• DDCU (Direct Current-to-Direct Current Converter Unit)

---

1. SARJ – Solar Array Tracking

• The SARJ node (sarj_mock.cpp) simulates rotation of the solar arrays to track the sun.
• It outputs a solar voltage estimate (/solar/voltage) that depends on the beta angle and sun position.
• This voltage serves as input to the BCDU to decide whether to charge batteries or switch to discharge mode (e.g., during eclipse).

---

2. Battery Manager

• Each channel (1–12) has two ORUs (Orbital Replacement Units), each with a BatteryManagementSystem (BMS).

• The battery_health.cpp node:

  • Publishes per-ORU sensor_msgs/BatteryState on /battery/battery_bms_<ID>/health.
  • Responds to /charge and /discharge service calls (simulated trigger-based).
  • Applies voltage drop/gain based on activity.
  • Rejects unsafe commands based on voltage limits (e.g., over 120 V or under 70 V).

---

3. BCDU – Charge/Discharge Controller

• Implemented as a ROS 2 action server in bcdu_device.cpp.

• Listens to:

  • Action goals on /bcdu/operation (charge or discharge with target voltage).
  • /solar/voltage topic to determine when to switch between charge/discharge.
  • Battery status from all 24 BMS instances.

• Parallelizes charge/discharge commands to all healthy ORUs via /battery/battery_bms_X/charge and /discharge.

• Publishes status to /bcdu/status and diagnostics to /eps/diagnostics.

Key features:

• Fault isolation if current > 127 A or voltage outside safe range.
• Automatic safe mode entry on fault detection.

---

4. MBSU – Channel Selection and Routing

• Implemented in mbsu_distributor.cpp.

• Subscribes to:

  • /mbsu/channel_<N>/voltage — one per EPS channel (voltage derived from BCDU-dispatched ORUs).

• Maintains a live mapping of channel voltages.

• Periodically calls selectHealthyChannels():

  • Picks top 2 healthy channels (voltage > 120 V).
  • Publishes combined voltage average to /ddcu/input_voltage (simulating DDCU supply).
  • Publishes warning diagnostics if fewer than 2 healthy channels available.

Note: MBSU does not subscribe to BMS health directly anymore — it only relies on channel voltage published by BCDU.

---

System Flow

           [SARJ]
             │
     +───────▼────────+
     │   Solar Power  │
     │    Estimate    │
     +───────┬────────+
             │ /solar/voltage
         [BCDU Action Server]
         /bcdu/operation
        ┌────────┬────────┐
        │        │        │
    /charge  /discharge  Monitor all ORUs
        │        │
 ┌──────▼──┐ ┌────▼────┐
 │ Battery │ │ Battery │  ...
 │  BMS 0  │ │  BMS 1  │  etc.
 └─────────┘ └─────────┘
      │              │
  /health         /health
      ▼              ▼
[MBSU Node]
 └─ Subscribes to:
      /mbsu/channel_<N>/voltage
 └─ Publishes:
      /ddcu/input_voltage (to DDCU)
 └─ Health selection:
      choose top 2 channels

---

Diagnostics and Fault Handling

• Each node publishes to /eps/diagnostics using diagnostic_msgs/DiagnosticStatus.

• Faults include:

  • BCDU overcurrent/undervoltage.
  • Battery overcharge/undervoltage.
  • MBSU channel selection failure.

These diagnostics can be monitored in real-time by system status nodes or GUIs.

---

Usage Notes

• Channels are configurable via ROS 2 parameters (num_channels).

• Simulation parameters (voltage thresholds, current limits) are hardcoded but can be made dynamic.

• Nodes should be launched in the following order for full EPS simulation:

  ros2 run demo_eps sarj_mock
  ros2 run demo_eps battery_health
  ros2 run demo_eps bcdu_device
  ros2 run demo_eps mbsu_device