Inductive Power System for Autonomous Underwater Vehicles Tim McGinnis University of Washington, Applied Physics Lab Inductive Power System for Autonomous.

Inductive Power System for

Autonomous Underwater VehiclesTim McGinnis

University of Washington, Applied Physics Lab

Inductive Power System for

Autonomous Underwater VehiclesTim McGinnis

University of Washington, Applied Physics Lab

• Major Components– Seafloor Secondary Node with Sensors– Subsurface float at 200m depth with Secondary Node and Sensor Suite – Mooring profiler with sensor suite that can “dock” for inductive battery

charging– 1700m electro-optical seafloor extension cable with E-O Converters– 800m electro-optical mooring cable with E-O Converters

• Features– Cable connection provides high power and real-time communications– Mooring profiler uses inductive modem for continuous comms– MARS compatible ROV-mateable Science Connectors on Float & Seafloor

Nodes– ROV servicing and installation of sensors

• Deployments– 2007 in Puget Sound at Seahurst Observatory in 30m water depth– 2008 on MARS in 950m water depth

ALOHA-MARS Mooring Sensor Network

Inductive Power System Requirements

• Needed to transfer several hundred watts to profiler

• Could not generate enough mate/unmate force for connectors

• Preferred non-conductive technique due to conductive medium

• Decided to use inductive transfer

S&K Engineering

• Principals had worked in the Electric Vehicle (EV) industry

• Working with US Navy on underwater inductive power transfer technology

DC-HFAC Driver (in Float Pressure Housing)

HFAC-DC Rectifier (in Vehicle Pressure

Housing)

Vehicle Battery Housing

EMI Filter/Transient Protection

Input150-400Vdc

Primary SideUnderwater

Coupler

Resonant Converter

BoostRegulator

In-Rush Current

Limit

Secondary Side

UnderwaterCoupler

400Vac50kHz

Driver Side Controller

Active Rectifier

Secondary Side

Controller/Li-Ion

Battery Charger

16.4VdcLithium Battery

Pack

Loads

Voltage Regulator

12V

Block Diagram

• Powered from 375VDC from MARS Node

• Driver chops input at 50kHz

• AC signal transferred across couplers

• AC signal rectified & regulated to 16.4VDC

• Microcontroller manages Lithium-Ion charging profile

Maximum Output Power vs. Gap

Maximum Output Power at 14.6Vdc

0

50

100

150

200

250

300

350

0 1 2 3 4 5 6Physical Gap mm

Ou

tpu

t P

ow

er

Wa

tts

0.64

0.66

0.68

0.7

0.72

0.74

0.76

0.78

0.8

0 1 2 3 4 5 6

Physical Gap mm

Eff

icie

nc

y

14Vout 140 Vin

16Vout 140Vin

18Vout 140Vin

14Vout 240Vin

16Vout 240Vin

18Vout 240Vin

20Vout 240Vin

Efficiency vs. Gap and Output Voltage

4 cell Lithium-Ion battery pack charging profile5 packs in parallel require 15A charging current

0

2

4

6

8

10

12

14

16

18

0:00

0:05

0:32

1:20

1:54

3:20

5:30

5:44

6:03

Elapsed Time

Vo

lts/

Am

ps Voltage

Current

Li-Ion Battery Charging Profile - constant current to 16.4V then constant voltage

Battery discharge profile at different loadsvoltage is reasonable indicator of capacity

Vout(t)

VISEC(t)

Gate Drive

Active Rectifier

V1

ISEC

PICMicrocontrollerIout(t)

PWMLowPass Filter

+

Vout(t)

-

Iout(t)

+

--

+

Synchronous Ramp

Reference

Vout(t)

VISEC(t)

Gate Drive

Active Rectifier

V1

ISEC

PICMicrocontrollerIout(t)

PWMLowPass Filter

+

Vout(t)

-

Iout(t)

+

--

+

Synchronous Ramp

Reference

Limit switch to indicate profiler in dockSpring shock absorber

Preparing for deployment in Puget Sound

Profiler with inductive couplers (docked)

in the water

Operation

• Profiler is programmed with minimum voltage (15V) – allowing 25-30% battery capacity remaining

• When profiler detects voltage below minimum, it returns to charging dock

• IPS driver turns on every minute – if current is flowing it continues to operate, if no current it turns off

• Profiler is programmed with minimum current (3A)• When minimum current is reached, profiler

resumes profiling• IPS turns off at 1.5A to prevent over-charging if

profiler present

Results of 2 month Deployment

• Deployed June 26, 2007

• Driver FET Failure on Aug 27, 2007

• Completed 4984 profiles

• Charge interval was approximately 7-8 days

• Currently investigating reason for FET failure

Current Status

HOT Profiling Mooring• Hawaii Ocean Time-

series (HOT) site• No cable to shore –

large battery pack• Iridium, FreeWave,

Acoustic Modem comms• 5000m water depth• Test deployment in

Puget Sound 2008• HOT deployment in 2009

Future Plans

• Implement “fuel gauge” – challenging to do with multiple charge/discharge cycles

• Utilize Smart Battery Data (SBD) available over System Management Bus (SMB)

• Improve efficiency by:– Modulate switching frequency with current– Optimize gap

• Make profiler & coupler ROV removeable

Questions?