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Sea-level simulator

CANopen inverter drives the 1,7-m impellors

Published 2018-01-12

ABB has equipped the circular wave and tidal current test facility located at the University of Edinburgh’s King’s Buildings campus. This includes CANopen-connectable inverters.

The circular wave and tidal current test facility at the University of Edinburgh is equipped with CANopen inverters (Photo: ABB)

The ACS800 inverters drive the 1,7-m impellors. The impellors are directly driven by a permanent magnet synchronous motor, which is speed-controlled by the 46-kW/60 kVA drive unit. The inverters are connected via CANopen to a third-party host controller. The bespoke impellors can each move more than five tons of water per second. The university required drives that did not need any encoder feedback, so as to reduce any additional cabling or devices underwater. ABB’s direct torque control is a sensorless motor control platform that provides the permanent magnet motors with low speed and torque accuracy, within one percent of demand; thereby recognizing the rotation without any position feedback devices.

The world’s first circular wave and tidal current test facility is located at the University of Edinburgh’s King’s Buildings campus. The ocean energy research facility comprises a 25-m diameter test tank. A central floor section, 15 m in diameter, lifts above the water. The facility is designed for sophisticated testing of wave and tidal energy devices and projects, fixed and floating offshore wind structures, and other marine technologies by applying scaled equivalents of waves up to 28 m high and currents of up to 14 knots. The tank is used for testing and de-risking marine energy technologies and projects at between 1/10th and 1/40th scale. Until now, device developers had to test their designs at around 1/100th scale, and then immediately faced the leap to quarter or full scale testing at sea – with all the associated cost and risk.

The circular shape, ringed with absorbing wave maker paddles, means waves have no reflections, allowing multi-directional wave and current generation for sophisticated model testing of renewable energy devices. The university awarded the main technical installation contract to Edinburgh Designs Limited, a world leader in hydrodynamic test equipment. The Flowave Ocean Energy Research Facility is managed by the Flowave university subsidiary company.

The ABB servo drives and motors and variable-speed drives are used to generate long-crested straight waves and fast currents. The computer control system combines thousands of these simple sine waves together to build a fully controllable ‘random sea’ that ABB says is 99,9 % representative of real sea conditions. Down either side of the tank hall, 30 m of marshaling cabinets house ABB circuit breakers, contactors, relays, switches, fuses, programmable logic controllers, servo-drives and variable-speed drives.

A ring of 168 wave maker paddles encircles the tank. The paddles create and also absorb waves. Each paddle has a robust brushless AC servomotor that drives a belt running over a curved guide on the top of the paddle. The BSM brushless servo motors are used to provide the full torque from zero speed with dynamic performance, as well as avoiding the wear and subsequent replacement of brushes, thereby reducing the cost of maintenance. The velocity, position, and force feedback of each paddle is controlled by ABB’s Motiflex e100 servo drive connected to a Powerlink network.

The 28 VSDs (variable speed drive) are housed in electrical cabinets situated alongside the tank. The drives are packed in close proximity within the cabinets and to help save space, a common busbar system is used to transfer the three-phase power to all of the drives. Each drive is given a different speed reference and it uses its internal logic and control systems to make the sensorless vector motors rotate at the speed needed to generate the linear profile of current in the water.