NASA Logo, National Aeronautics and Space Administration

EPS Testbed Hardware

The EPS can deliver AC (Alternating Current) and DC (Direct Current) power to loads, which in an aerospace vehicle would include subsystems such as the avionics, propulsion, life support, and thermal management systems. The schematic below depicts ADAPT’s major system components and their interconnections. Three power generation sources are connected to three sets of batteries, which in turn supply two load banks. Each load bank has provisions for 6 AC loads and 2 DC loads.

Power Generation: Two battery chargers can be interchangeably connected to the three batteries. Hardware relay logic prevents connecting one charge source to more than one battery at the same time, and from connecting one charging circuit to another charging circuit. Additional means for power generation, such as generators and photovoltaic cells, are being investigated.

Power Storage: Three sets of batteries are used to store energy for operation of the loads. Each “battery” consists of two 12-volt sealed lead acid batteries connected in series to produce a 24-volt output. Two battery sets are rated at 100 amp-hrs and the third set is rated at 50 amp-hrs. Possible extensions in this area include the incorporation of Lithium ion batteries to produce a 28.8 volt output, which is typical of aircraft DC power.

Power Distribution: Electromechanical relays are used to route the power from the sources to the batteries, and from the batteries to the AC and DC loads. All relays are of the normally-open type. An inverter converts the 24-volt DC battery input to a 120-volt rms AC output. Circuit breakers are located at various points in the distribution network to prevent overcurrents from causing unintended damage to the system components. Future enhancements in power distribution could include additional voltage levels envisioned for future aircraft and spacecraft electrical power systems.

Control and Monitoring: Testbed data acquisition and control use National Instrument’s LabVIEW software and CompactFieldPoint (cFP) and CompactRio (cRio) hardware. The instrumentation allows for monitoring of voltages, currents, temperatures, switch positions, light intensities, and AC frequencies. Over a hundred sensors report the status of the system to the diagnostic application that monitors the health status of the system.

Sample data from the system may be found on DASHlink.

diagram

click to enlarge

Fault Injection

A key aspect of the testbed is providing a controlled environment to inject faults, either through software or hardware, in a repeatable manner. This facilitates assessing the effectiveness of the technologies in terms of technical performance metrics. The EPS testbed supports the injection of faults in three ways:

Hardware-Induced Faults: These faults are physically injected at the testbed hardware. A simple example is tripping a circuit breaker using the manual throw bars. Another is using the power toggle switch to turn off an inverter. Faults may also be introduced in the loads attached to the EPS. For example, the valve can be closed slightly to vary the back pressure on the pump and reduce the flow rate.

Software-Induced Faults: Faults may be introduced via software in one or more of the following ways: (1) sending commands to the testbed that are not intended for nominal operations; (2) blocking commands sent to the testbed; and (3) altering the testbed sensor data.

Real Faults: In addition the aforementioned two methods, real faults may be injected into the system by using actual faulty components. A simple example includes a burned out light bulb.

Diagnostic Challenges

The ADAPT EPS testbed offers a number of challenges to diagnostic algorithms:

  • Hybrid system with many modes of operation due to switching elements such as relays and circuit breakers
  • Continuous dynamics within operation modes and components from multiple physical domains, including electrical, mechanical, and hydraulic
  • Multiple-faults
  • Timing considerations and transient behavior must be taken into account (e.g., delay of a few seconds to provide inverter output power; current transient when loads are connected)
  • Sensor noise depends on loads attached and exhibits occasional spikes
  • Limited sample rates

First Gov logo
NASA Logo - nasa.gov