29-12-2012, 06:06 PM
Inductive Power System for Autonomous Underwater Vehicles
Inductive Power System.pdf (Size: 697.19 KB / Downloads: 63)
INTRODUCTION
The ALOHA-MARS Mooring (AMM) project will
demonstrate the scientific potential of combining a mooring
profiler vehicle with a moored deep-ocean sensor network for
connection to a seafloor observatory with power and
communications provided from shore via an electro-optical
cable. . This system
will address the challenge of sampling the ocean with high
temporal and vertical resolution over time scales that are not
possible with a standard, non-rechargeable battery pack. The
mooring sensor network will consist of three main
components: a near-surface float at a depth of 160 m with a
secondary node and suite of sensors; an instrumented
motorized mooring profiler moving between the seafloor and
the float; and a secondary node on the seafloor with a suite of
sensors. Both secondary nodes have ROV mate-able
connectors available for connecting the basic sensors and
additional guest instruments. The profiler will have real-time
communications with the network via an inductive data
modem that will allow science data transmission and remote
control functions.
HFAC-DC Rectifier
The HFAC-DC Rectifier converts the HFAC power to
direct current for charging the battery. The Rectifier has a
micro-controller that controls the battery charging voltagecurrent
profile appropriate for a Lithium-Ion battery. The
charging starts out in constant current mode and can supply a
charging current of approximately 15A. When the battery
voltage reaches about 16.4V, the controller switches to a
constant voltage mode.
The MMP is programmed to terminate the charge when the
charging current drops below 1.5A - 10% of the initial current.
Again, a copper plate attached to backside of the circuit board
conducts 20 W of waste heat to the endcap.
A similar topology was developed and standardized for
inductive charging of electric vehicles (EV). In the EV
application, a communication loop was established between
the battery side systems and the primary side by which the
operating frequency was varied to control the voltage and
current delivered to the battery to implement specific battery
charging algorithms. In the EV application, communication
initially was implemented with an RF carrier and later on an
infra red (IR) carrier. Both of these technologies encounter
difficulties for long term implementation in sea water. In this
converter, power delivery is controlled by a FET switch on the
secondary side, as shown in Figure 3. Communication
between the primary and secondary sides of the system is not
required. The inductive coupler when driven by the series
resonant inverter looks like a high frequency constant current
source. The switch is operated synchronously with the
secondary current waveform.
Operational Results
The ALOHA-MARS Mooring system was deployed in Puget
Sound in June 2007. Through the first two months of operation, the
MMP and inductive charger were generally working as expected.
The profiler vehicle has sufficient battery capacity to operate for
about a week and when the battery voltage gets below a remotely
configurable voltage, the vehicle initiates a “charge” sequence and
proceeds to the charging dock. An over-ride ‘charge’ command can
also be sent over the inductive comms ling to initiate the charge
sequence.
The IPS includes a circuit to minimize the in-rush current when the
system is energized and this circuit may need some improvement
because we have had some instances of voltage drop due to high
current transients in the long cables.
More testing needs to be done on the circuit that determines
whether the secondary is connected and either leaves the driver on or
turns it off. In some cases, the driver has remained on when it should
have shut off.