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Publication Date: 2015-Feb-09
Document File: 2 page(s) / 26K

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Matti Kivioja: INVENTOR [+3]


The suggestion is to harvest the deacceleration kinetic energy of an azimuthing propulsion unit with energy recovery system installed to the intermediate circuit of frequency converter and use it later on when there is a demand for it (re-acceleration). The energy efficiency of the steering system is significantly improved.

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In Electrical Steering System the azimuthing propulsion unit, such as Azipod unit, helm angle is controlled with four frequency controller controlled induction motors. This means, that the ener- gy that is needed to overcome the hydrodynamic forces, inertia and friction in the system is fed by the induction motors.

The energy needed to accelerate the Azipod unit to a constant turning motion (e.g. 2,5 deg/s) can be seen as load in the electrical motors. However, when the Azipod unit has achieved a constant turning motion and it needs to be stopped, the kinetic energy stored to the system
has to be handled somehow. This means, that while the Azipod unit is being deaccelerated, the electrical motors are acting as generators because their rotational direction is opposite to
the torque that they are generating. This situation will cause the frequency converters intermediate DC-voltage to rise because the energy flowing from the motors towards the frequency converter. In order to prevent the frequency converters from tripping to high DC-voltage, we have to direct the excessive voltage to braking resistors via brake chopper circuit.

The method described above is very energy inefficient, because all kinetic energy stored to the steering system is dissipated to thermal energy in the braking resistors.

Our suggestion is to harvest this kinetic energy with energy recovery system installed to the intermediate circuit o...