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

2. ALOHA-MARS Mooring Sensor Network Major Components Features
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

4. 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

5. S&K Engineering
Principals had worked in the Electric Vehicle (EV) industry
Working with US Navy on underwater inductive power transfer technology

6. 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

8. Maximum Output Power vs. Gap
Maximum Output Power at 14.6Vdc 50
100
150
200
250
300
350 1 2 3 4 5 6
Physical Gap mm
Output Power Watts
Maximum Output Power vs. Gap

9. Efficiency vs. Gap and Output Voltage

10. 4 cell Lithium-Ion battery pack charging profile
5 packs in parallel require 15A charging current

11. Li-Ion Battery Charging Profile - 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
Volts/
Amps
Voltage
Current
Li-Ion Battery Charging Profile -
constant current to 16.4V then constant voltage

12. Battery discharge profile at different loads
voltage is reasonable indicator of capacity

14. Limit switch to indicate profiler in dock
Spring shock absorber

15. Preparing for deployment in Puget Sound

16. Profiler with inductive couplers (docked)
in the water

17. 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

18. 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

19. Current Status

20. 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

21. 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

22. Questions?