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NEPTUNE Power System
Low Voltage Circuit
Preliminary Design Review
Tim McGinnis
Dec 4-5, 2003
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
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
PARAMETER
Input Voltage:
External Load Control
Number of External Loads
400VDC
48VDC
Internal Load Control
Number of Internal Loads
48VDC
+5, +/- 12VDC
Ground Fault Detection
Ground Fault Isolation
Over-current Protection
Isolation between circuits
Seawater ground isolation
Surge and Spike Protection
Noise Filtering
SPECIFICATION
48 VDC & 400VDC
8
9.2 kW (22.5A) to any or all loads
(includes 48V External Loads)
1.2 kW (25A) to any or all loads
16
100W (2A) to any load, 800W total
TBD
100 μA
Full galvanic
Programmable by user
>XX V
> XX MΩ
VERIFICATION
Testing
Testing
Testing
Testing
Testing
Testing
Testing
Design and Testing
Design and Testing
Design and Testing
Design and Testing
Mechanical Requirement
PARAMETER
Thermal Management:
Dimensions
Connectors
Mounting
REQUIREMENT
Immersed in Flourinert
TBD
TBD
TBD
COMPLIANCE
Analysis and Testing
Design
Design
Design
Environmental Requirement
PARAMETER
Temperature range
EMC and EMI
Shock and vibration
REQUIREMENT
per Neptune Power System
Requirement Document
per Neptune Power System
Requirement Document
per Neptune Power System
Requirement Document
COMPLIANCE
Analysis and Testing
Analysis and Testing
Analysis and Testing
Mission Assurance Requirement
PARAMETER
Lifetime
REQUIREMENT
30 years
FIT Rate
1000 FITS (?)
COMPLIANCE
Design, Modeling and
Accelerated Life Testing
Design, Modeling and
Accelerated Life Testing
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
2 - 400V
2 - 48V
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
I
400VDC
I
48VDC
Science Connector
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
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)
External Load Control & Monitoring
Device
Rating
(V)
PD @ 25A
RDS(on) (Ω)
(W)
2 devices
in parallel
(W)
4 devices
in parallel
(W)
8 devices
in parallel
(W)
100
0.009
5.6
1.4
0.4
0.09
200
0.02
13
3.1
0.8
0.20
500
0.08
50
12.5
3.1
0.78
600
0.13
81
20.3
5.1
1.27
800
0.25
156
39.1
9.8
2.44
1000
0.40
250
62.5
15.6
3.91
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
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 = 48W @ 73W = 1.5A
– DCS Router = 12V @ 165W = 13.8A
• Switching can be accomplished with single MOSFET
devices
Low Voltage Power Requirements
(Preliminary)
(in Watts)
Fiber Optics Equipment
+5V
50
Communications Routers
Controller
+12V
300
350
15
10
Sensors
24
Relays
22
Totals
+48V
65
406
300
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 overcurrent 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
400VDC
400V
External
Loads
400VDC
input
400RET
48VDC
400V-48V
DC-DC
converter
48V
External
Loads
48RET
Iso
Amp
48V-12V
DC-DC
converter
Iso
Amp
Iso
Amp
12V
-12V
Node Control Circuitry
48V-5V
DC-DC
converter
5V
Internal Circuit Isolated
from External Circuits
0V
12V
Internal
Loads
400V-48V
DC-DC
converter
???
48V
Internal
Loads
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