NEPTUNE Power System Low Voltage Circuit

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NEPTUNE Power System Low Voltage Circuit

• Preliminary Design Review
• Tim McGinnis
• Dec 4-5, 2003

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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

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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 lt100 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.

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Power System Specifications (contd)

• 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.

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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 gtXX V Design and
  Testing
• Seawater ground isolation gt XX MO Design and
  Testing
• Surge and Spike Protection Design and Testing
• Noise Filtering Design and Testing

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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
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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

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400V 48V Bus Voltage Monitoring

• Resistor Voltage Divider
• Isolation Amplifier to maintain isolation between
  400V and Controller

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48V5/12V 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

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COTS/MIL Level DC-DC Converters

• High MTBF
• MIL Qualification
• Environmental Stress Screening on each module

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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

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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

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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

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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

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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

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External Load Control Monitoring

• Heating problem with MOSFETs can be reduced by
• Paralleling devices
• 600V relay has RDS(on) of 0.13O
• 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)

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External Load Control Monitoring
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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

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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
  100s

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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

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Internal Load Control

• Do not need isolation or deadface relays
• Maximum current through any device
• Optical Equipment 48W _at_ 73W 1.5A
• DCS Router 12V _at_ 165W 13.8A
• Switching can be accomplished with single MOSFET
  devices

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Low Voltage Power Requirements(Preliminary)
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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

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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

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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