Self-contained power conversion
module for wave energy applications
BPS 2016 ©
What is it ?
O-Drive is a self-contained module that converts
mechanical energy into grid-quality AC electricity.
It is designed for use in ocean wave energy
applications.
Ocean swell waves typically have periods of 6-14
seconds, and most wave energy devices are
designed to oscillate or reciprocate in sync with
the wave motion. Generally, the wave energy
device captures energy from the wave field,
converting it into mechanical energy at the “shaft”.
The main challenge in wave energy has been
to convert this mechanical energy into useable
electricity. Due to the slow rate of movement and
the reversal of direction with every passing wave,
the use of gearboxes and rotary motors is not
practical.
O-Drive solves the problem by using conventional
high-pressure hydraulic equipment to convert
the mechanical energy into pressure energy and
kinetic energy carried by the working fluid within
a controlled hydraulic circuit. This closed circuit
system receives an unsteady, and irregular,
supply of energy from the mechanical system
by way of one or more interconnected hydraulic
cylinders. The high-pressure flow within the
circuit is regulated by a unique arrangement of
accumulators, controllable valves, and a variable
displacement hydraulic motor.
Flow through the hydraulic motor results
in conversion of energy into uni-directional
constant-speed shaft power. The hydraulic motor
is directly coupled to an asynchronus electrical
generator, with electrical output delivered to an
onboard line module synchronised with the grid.
Essentially, the O-Drive injects smooth 3-phase
AC-electricity into the grid at the line frequency.
O-Drive is the “heart and brain” of the wave
energy system.
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Key Features
• O-Drive is a self-contained module, with
standard inputs and outputs, easily adapted to
any wave energy technology,
• O-Drive automatically handles all power
regulation and conditioning, ensuring smooth
grid-compatible AC electricity is delivered,
• Optionally, in-built auxiliary hydraulic power pack
for control and actuation of external mechanisms
or valves on the wave energy device,
• Optionally, in-built step-up tranformer, for
export of high-voltage AC electricity to shore,
thus minimising transmission losses,
• Built-in proprietary “ride-through” capability, to
maintain constant power output during lulls or in
between wave sets,
• Complete in-built and integrated handling
of all sensors and data for the whole of plant,
including data management, buffering, storage
and realtime delivery to onshore proprietary
database and visualisation tool,
• Built-in proprietary “shedding” capability, to
maintain constant power output when wave
energy input exceeds grid request or is higher
that machine peak rating,
• Continuous real-time monitoring of all system
sensors, equipment and power metrics, via
internet enabled communications, allowing full
system access from any location,
• Complete machine control, Human-machineinterface (HMI) and SCADA systems fully
integrated and in direct communication to shore
via fibre-optic link,
• Configurable to receive instantaneaous power
in excess of 1MW (at peak pressure and flow),
and maintain steady continuous output of up
250kW (with 10% over-load protection).
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Development
O-Drive was developed under a 5-year $10,000,000 project funded by BPS and AusIndustry, between
2007 and 2012. Two complete O-Drive units were built and tested at BPS’ facilities in Sydney.
These units were rigorously tested in a configuration that used two double-acting (power delivery on
both instroke and outstroke) hydraulic cylinders for producing the hydraulic flow into the O-Drive. In
order to test the O-Drive under simulated ocean conditions, a second pair of cylinders was used to
oppose the primary pair, with the secondary pair applying the dynamic forces to simulate those that
would occur in the ocean. Both pairs of cylinders were assembled into a steel frame with a central
rotary linkage between them. This configuration allowed full-scale irregular ocean wave forces to be
applied to the cylinders under test. A second O-Drive module was used as a pump, with a unique
programmable valve arrangement, to deliver the hydraulic power to the ‘driving’ cylinders. By testing
in this way, power was drawn from the grid to create the simulated ocean, and the mechanical power
converted back into electricity was then fed back into the local grid by the O-Drive.
Below image (bottom left and background left): Assembly of two O-Drive hydraulic-electric
modules, with all components fitted in cartridge frames (2009).
Below image (centre): Hydraulic cylinder frame under construction (2009)
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BPS used standard off-the-shelf hydraulic and electric components, but assembled these in
a unique proprietary way to complete the O-Drive. The whole of machine control functionality
was developed based on a set of discrete functions. These were programmed and interfaced
with hardware-level instructions. The entire function library was then used to build operational
algorithms. These algorithms are programmed in standard PLC languages, and serve to control
the machine and allow user input. Functionality is provided to allow autonomous operations,
whereby the O-Drive can function and generate electricity to the grid with no user intervention.
A platform-independent user interface was developed, based on internet protocols, such that an
O-Drive can be monitored and managed from any location.
Above image: O-Drive “test unit”, capable
of driving a full-scale 250kW O-Drive under
simulated full-load wave conditions. This
set up was used to refine the mechanical
and hydraulic systems, including adjustment
of valve timing and overall function. The
facility also provided a convenient platform
for development of software for control and
monitoring (2012).
BPS 2016 ©
Left image: O-drive has been fully integrated
into a bioWAVE ocean wave energy device,
for operation at an ocean site in Australia. All
system function, hydraulic connections, and
general operability tests were witnessed and
verified by DNV GL (2015).
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Operation
O-Drive is designed to be fitted to a wave energy device, and then connected to one or more
hydraulic cylinders on the device that receive energy from the motion of the main device structure.
More than one O-Drive can be installed on a single large wave energy device. Multiple O-Drives
allow for flexibility when larger output capacity is required, and provide for redundancy when a high
level of reliability is required. Alternatively, several small wave energy devices can be connected to
a single O-Drive, allowing the energy collected from a cluster of wave energy devices to be delivered
to shore as one supply on a single cable.
Each O-Drive is fully programmable and autonomous. In addition to managing and delivering the
flow of electricity to shore, the O-Drive can be used to automatically control auxiliary electric and
hydraulic equipment (such as valves, latches, releases, pumps, levers, sensors or other ‘smart’
devices).
O-Drive can manage start-up and shut-down sequences automatically. Proprietary algorithms and
software systems, developed by BPS, can be configured such that O-Drive is able to self-monitor
on-coming (forecasted) wave conditions using a combination of local real-time measurements and
far-field weather/wave modelling, allowing shut-down or start-up events to be triggered automatically.
A thorough multi-layered logic system is used to monitor system alarms and failures, with safety
shut-downs fully configurable.
O-Drive has met all requirements and been certified for operation as an embedded generator the
regional NEM grid operator (PowerCor) and regulator Energy Safe Victoria (Australia).
Below image: O-Drive installed on subsea bioWAVE device at Port Fairy, Australia (2015).
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Maintenance
For the purpose of the bioWAVE Project at Port Fairy, BPS developed a purpose-built “Retrieval Rig”,
designed to retrieve an O-Drive module from the ocean site, and to bring it onshore for maintenance.
The Retrieval Rig provides for a convenient method of maintaining the O-Drive, without the need to
bring the entire wave energy device (in this case, bioWAVE) to shore.
Above image: O-Drive with internal ‘cartridge’ removed. The complete intact equipment frame,
assembled as a ‘cartridge’, can be pulled out of the O-Drive pressure vessel, directly on to a purposedesigned rollable frame. The entire assembly can then be re-located for convenient servicing.
Below image: BPS maintains a detailed 3D CAD model of the O-Drive, including all components.
All parts and components are catalogued, allowing for efficient ordering of replacement parts or
spares.
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Technical Specifications
Electrical
• Rated continuous power output: 250kW
• Generating voltage: 415V AC
• Export voltage (optional tranformer): 3.3kV AC (as built)
• System: Asynchronus machine, 3-phase inverter
• Efficiency of electrical system (shaft to terminals) at rated power: 92%
Hydraulic
• Flow rate (continuous at rated power): 400 cm3/rev at 1600rpm
• System pressure normal operating range: 150-350 bar
• Variable displacement hydraulic motor, logic control valves
• Efficiency of hydraulic system at rated power (continuous flow): 88%
O-Drive
• Overall O-Drive efficiency at rated power (continuous flow): 80%
Notes
Actual efficiency will be lower at lower power levels, due to on board consumption. Efficiency values
noted above are for continuous hydraulic flow. Most wave energy devices do not provide continuous
hydraulic flow, so time-averaged efficiency may be lower depending on number of cylinders used,
single- or double-acting, duration of zero- or low-flow during motion reversal, and cylindar mode
switching.
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Contact
BPS
Unit 11
40-42 O’Riordan Street
Alexandria, NSW 2015
Australia
Ph: +61 2 9146 4420
Email: [email protected]
Web: www.biopowersystems.com
BPS 2016 ©
BioPower Systems Pty Ltd
ABN 65 118 641 562
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