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

NEPTUNE Low Voltage Requirements SPE1Average 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. SPE41.3 kW of 48VDC power shall be available to the Node Science Connectors at each node. Note: Assumes 700W internal load

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.

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.

Electrical Specifications PARAMETERSPECIFICATIONVERIFICATION Input Voltage:48 VDC & 400VDCTesting External Load Control Number of External Loads8 400VDC9.2 kW (22.5A) to any or all loadsTesting (includes 48V External Loads) 48VDC 1.2 kW (25A) to any or all loadsTesting Internal Load Control Number of Internal Loads16 48VDC100W (2A) to any load, 800W totalTesting +5, +/- 12VDCTBDTesting Ground Fault Detection100 μATesting Ground Fault IsolationFull galvanic Over-current ProtectionProgrammable by userTesting Isolation between circuits>XX VDesign and Testing Seawater ground isolation> XX MΩDesign and Testing Surge and Spike ProtectionDesign and Testing Noise FilteringDesign and Testing

Mechanical Requirement PARAMETERREQUIREMENTCOMPLIANCE Thermal Management:Immersed in Flourinert Analysis and Testing Dimensions TBDDesign Connectors TBDDesign MountingTBDDesign Environmental Requirement PARAMETERREQUIREMENT 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 PARAMETERREQUIREMENT COMPLIANCE Lifetime 30 yearsDesign, Modeling and Accelerated Life Testing FIT Rate1000 FITS (?) Design, Modeling and Accelerated Life Testing Mission Assurance Requirement

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

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

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

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

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

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

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

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

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

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

Device Rating (V)R DS(on) (Ω) P 25A (W) 2 devices in parallel (W) 4 devices in parallel (W) 8 devices in parallel (W) External Load Control & Monitoring

Paralleling MOSFETS requires good current sharing Need to select parts with similar R DS(on) and good PCB design R DS(on) goes up with temperature so there is some inherent current balancing 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

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

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

Low Voltage Power Requirements (Preliminary) (in Watts)+5V+12V+48V Fiber Optics Equipment Communications Routers 350 Controller1510 Sensors 24 Relays 22 Totals

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

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

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