NEPTUNE Power System

Low Voltage Circuit

Preliminary Design ReviewTim McGinnisDec 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 SPECIFICATION VERIFICATIONInput Voltage: 48 VDC & 400VDC TestingExternal Load Control

Number of External Loads 8400VDC 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 ControlNumber of Internal Loads 1648VDC 100W (2A) to any load, 800W total Testing+5, +/- 12VDC TBD Testing

Ground Fault Detection 100 μA TestingGround Fault Isolation Full galvanicOver-current Protection Programmable by user TestingIsolation between circuits >XX V Design and TestingSeawater ground isolation > XX MΩ Design and TestingSurge and Spike Protection Design and TestingNoise Filtering Design and Testing

Mechanical RequirementPARAMETER REQUIREMENT COMPLIANCEThermal Management: Immersed in Flourinert

Analysis and Testing

Dimensions TBD DesignConnectors TBD DesignMounting 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

PARAMETER REQUIREMENT COMPLIANCE

Lifetime 30 years Design, Modeling and Accelerated Life Testing

FIT Rate 1000 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

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

S

cien

ce C

onne

ctor

I

I

400VDC

48VDC

• 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) RDS(on) (Ω)PD @ 25A

(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

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) +5V +12V +48V

Fiber Optics Equipment 50   300

Communications Routers   350  

Controller 15 10  

Sensors   24  

Relays   22  

Totals 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 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

400V-48VDC-DC

converter

48V-5VDC-DC

converter

48V-12VDC-DC

converter

48VDC

48RET

Node Control Circuitry

12V

0V

5V

400VDC

400RET

IsoAmp

IsoAmp

400VExternalLoads

48VExternalLoads

400VDCinput

-12V

12VInternalLoads

48VInternalLoads

IsoAmp

400V-48VDC-DC

converter???

Internal Circuit Isolatedfrom External Circuits

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