DC Grid with Energy Storage for Jack-up rigs
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- Institutt for elkraftteknikk 
Energy storage systems are used in various applications to compensate for a fluctuating power demand. For a jack-up drilling rig, energy storage can work as a buffer between load motors and diesel generators. During a tripping operation, which involves lifting and lowering of the drill string, the diesel generators limits how fast the motor loads can accelerate. The objective of the work presented in this thesis, was to build a model for simulations of DC grid with energy storage and use this model for a case study to answer how much an energy storage can speed up the operation, and which energy storage technology that is best suited for the purpose.The studied system was a DC grid for jack-up rigs supplied by diesel generators. Two energy storage technologies were considered; electrolytic capacitors and super-capacitors. The main basis of comparison between these technologies was power- and energy density.When performing a tripping operation, the load motors have a repeating and fluctuating power demand which changes throughout the operation depending on how heavy the load is. The energy storage will supply the increasing load power while the diesel generators accelerate. It was decided to investigate two scenarios which repeat throughout the tripping process; one for high load, and one for low load.Several simplifications were made when building a model in Simulink. The model consisted of one diesel generator model, several energy storage modules with DC-DC converters, and a load model. The loads were modelled as a current source which draws a given power based on the measured voltage. The diesel engine was modelled as a first order system, while the generator was modelled using a built in Simulink model. It was found that a two quadrant DC-DC converter was a suitable interface between the energy storage and DC bus. Two energy storage models were developed, one for supercapacitors and one for electrolytic capacitors.Four simulations were run to compare the two energy storage technologies and to investigate the two different load scenarios. The results indicated that an energy storage can reduce the time duration of a tripping operation with 11-16%. It was also found that the supercapacitors had the best power- and energy density for the studied load scenarios. Over all, the model worked properly and gave trustworthy results.