NEPTUNE Power System Low Voltage Circuit

1. NEPTUNE Power System Low Voltage Circuit Preliminary Design Review Tim McGinnis Dec 4-5, 2003

2. NEPTUNE Low Voltage Requirements • SPE1 Average and peak power delivery to the Node Science Connectors for a particular node shall not be less than 3.3 kW and 9.3 kW, respectively. • SPE3 Power delivery to the user shall be at two voltage levels: 48VDC and 400VDC. • SPE4 1.3 kW of 48VDC power shall be available to the Node Science Connectors at each node. Note: Assumes 700W internal load

3. Power System Specifications • Each 400V user circuit shall have a maximum current capacity of 23A (9300 W) that shall be available at any or all science connectors • Each 48V user circuit shall have a maximum current capacity of 27 A (1300 W) ) that shall be available at any or all science connectors • The Power System must be able to detect a ground fault of <100 µA on any of the science connector power conductors and to isolate that conductor from the internal power circuit. • All external circuits shall have a deadface switch that will provide galvanic isolation in the event of a ground fault.

4. Power System Specifications (cont’d) • The Power System shall have an interface to the Observatory Control System (OCS) which would allow users to define and schedule power settings such as power cycling, changes in power requirements, etc. • The Power System must be able to detect a over-current fault on any of the science connector power circuits and disconnecting the faulted circuit. The current limit will be set by the user through the OCS. • The Power System shall be capable of monitoring the total load requests for both of the output voltages and controlling the power to the loads so as not to exceed the Power System operating limits. • All circuits providing power to external loads will have isolation from each other, seawater and all internal circuits.

5. Electrical Specifications PARAMETER SPECIFICATION VERIFICATION Input Voltage: 48 VDC & 400VDC Testing External Load Control Number of External Loads 8 400VDC 9.2 kW (22.5A) to any or all loads Testing (includes 48V External Loads) 48VDC 1.2 kW (25A) to any or all loads Testing Internal Load Control Number of Internal Loads 16 48VDC 100W (2A) to any load, 800W total Testing +5, +/- 12VDC TBD Testing Ground Fault Detection 100 μA Testing Ground Fault Isolation Full galvanic Over-current Protection Programmable by user Testing Isolation between circuits >XX V Design and Testing Seawater ground isolation > XX MΩ Design and Testing Surge and Spike Protection Design and Testing Noise Filtering Design and Testing

6. Mechanical Requirement PARAMETER REQUIREMENT COMPLIANCE Thermal Management: Immersed in Flourinert Analysis and Testing Dimensions TBD Design Connectors TBD Design Mounting TBD Design Environmental Requirement PARAMETER REQUIREMENT COMPLIANCE Temperature range per Neptune Power System Analysis and Testing Requirement Document EMC and EMI per Neptune Power System Analysis and Testing Requirement Document Shock and vibration per Neptune Power System Analysis and Testing Requirement Document Mission Assurance Requirement PARAMETER REQUIREMENT COMPLIANCE Lifetime 30 years Design, Modeling and Accelerated Life Testing FIT Rate 1000 FITS (?) Design, Modeling and Accelerated Life Testing

7. LV Circuit Description • 400V & 48V bus voltage monitoring • 48V-5V/12V DC-DC Converter • External Load Control & Monitoring • Ground Fault Monitoring & Isolation • Internal Load Control & Monitoring

8. 400V & 48V Bus Voltage Monitoring • Resistor Voltage Divider • Isolation Amplifier to maintain isolation between 400V and Controller

9. 48V:5/12V Converter • Controller requires 5V, +/-12V • Relay control inputs require +12V • Current sensors require +/- 12V • Isolation amps require +/- 12V • DCS components require +12V • Need to confirm all voltage and power requirements • LV Converter PCB will use COTS/MIL level converter modules • Design will include 100% redundancy, minimize possibility of single point failures

10. COTS/MIL Level DC-DC Converters • High MTBF • MIL Qualification • Environmental Stress Screening on each module

11. External Load Control & Monitoring • 8 science connectors (4 for MARS) • 400V, max I = 23 A (9300 W) • 48V, max I = 27 A (1300 W) • Max current available at any single connector or the total of all connectors - typical current is much lower • Need power switching and current monitoring for both voltages on all connectors • Need to monitor ground fault current on both power busses • Need deadface relay on both legs for galvanic fault isolation

12. External Load Control & Monitoring • 8 Science Connectors • ROV/Underwater Mateable • Rated for 3000V/30A • ~10 conductors 2 - 400V 2 - 48V 4 - Ethernet 2 - Time Distribution

13. External Load Control & Monitoring • Solid state MOSFET switch • can interrupt DC current • non-zero off-state leakage – if cable cut, small fault current could result • non-zero on-state resistance – results in device heating

14. External Load Control & Monitoring • Mechanical relay • provides complete galvanic isolation • has near-zero on-state resistance • cannot interrupt DC current without arcing and damage to switch

15. External Load Control & Monitoring • Mechanical/Solid State Hybrid • Solid state switch to make/break current • Mechanical relay to provide galvanic “deadface” isolation in case of faulted instrument

16. External Load Control & Monitoring • Heating problem with MOSFETs can be reduced by: • Paralleling devices • 600V relay has RDS(on) of 0.13Ω • With single device I = 25A, PD = (25)2 * 0.13 = 81W • With 4 paralleled devices I = 25/4 A, PD = (6.25)2 * 0.4 = 5W • Operating the devices in liquid (Fluorinert)

17. External Load Control & Monitoring

18. External Load Control & Monitoring • Paralleling MOSFETS requires good current sharing • Need to select parts with similar RDS(on) and good PCB design • RDS(on) goes up with temperature so there is some inherent current balancing

19. External Load Control & Monitoring • NEPTUNE long life requirement may require hermetically sealed components • International Rectifier has proposed a module with: • 6 paralleled Hi-rel MOSFETS in hermetically sealed case • Entire die from single wafer • Good matching of key parameters • Less expensive than discretes in quantities of 100’s

20. Internal Load Control • Provide 12V & 48V power switching to internal loads • Optical transport equipment • Data Communications Network equipment • Controller • Time Distribution equipment • Engineering sensors • Power System electronics and sensors

21. Internal Load Control • Do not need isolation or deadface relays • Maximum current through any device: • Optical Equipment = 48W @ 73W = 1.5A • DCS Router = 12V @ 165W = 13.8A • Switching can be accomplished with single MOSFET devices

22. Low Voltage Power Requirements(Preliminary)

23. Over-current Protection • Controller would have maximum current setting from Observatory Control System • Over-current trip point can vary – lights or pump may turn on in response to an event • Controller monitors current and opens switch if over-current trip point exceeded

24. Ground Fault Monitoring • Difficult to protect individual user circuits if they all connect to 400V or 48V bus • Differential ground fault monitoring only sensitive to ~10mA • Most reasonable option for high sensitivity is to monitor bus potentials relative to seawater • If fault is detected, need to cycle power off to all loads to find faulted circuit • Users need to know about this potential load disconnection – may need to provide their own batteries

26. Status • Built prototype circuit board and dummy load for 1 science connector circuit • 48 V and 400V circuit with: • Current sensor • MOSFET switch 1 for 48V 6 in parallel for 400V • Mechanical deadface relay • MOSFETS run hot in air at rated current – need to test in Fluorinert