Modeling and control of hybrid marine power plants
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- Institutt for marin teknikk 
Recent advancements in energy storage devices technology, together with increased concerns and regulations on greenhouse gas emissions have been a major factor for the development of new and innovative marine power plants design and operation. This thesis focus on one particular operation of hybrid power plants, which is strategic loading. Due to the lack of readily available models and little understanding on this new emerging area, it was mandatory to study the viability of strategic loading on hybrid marine systems, as well as to evaluate exactly the potential for gas emissions mitigation and fuel consumption reduction due to the presence of the energy storage device. Initially, the effects of the power plant over the DP system were studied, analyzing how much the vessel performance can be improved by guaranteeing a more stable power supply. The energy storage device was analyzed more in depth, with two models being derived. The first model, a high fidelity hybrid dynamic model, captures the fact that the energy storage device time constant is much smaller than the mechanical components, such as engines, thus, being modeled as a discrete event system. The validity of the hybrid dynamic model is validated with experiments conducted in the Hybrid Machinery Laboratory at NTNU, where it is shown that the derived model accurately describes the real system, and can be used to model hybrid power plants with strategic loading. Due to the high complexity and the fact that the hybrid dynamic model is computational demanding, a second model is derived, where the steady state values are taken into account. It is derived such that the resulting average fuel consumption and average gas emissions are a weighted average of the set-points defined by the strategic loading. The hybrid dynamic model is used to validate the steady state model and shows that both models present a high correlation, specially in cases where the transient effects are much faster than the steady state, as expected. With the steady state model, two optimization strategies were derived, that could be used either to minimize fuel consumption or minimize gas emission. The first optimization consists of the active set method, which is proven to converge quickly to the optimum solution in case the discrete mapping from the genset is interpolated linearly. The second optimization strategy, the interior point method, is recommended in case higher order interpolation methods are used to describe the engine characteristic curves, but it has the drawback of being computationally intensive. By combining both optimization strategies, it is possible to have the best performance, being able to operate in real time, while the higher order interpolation methods are respected. It lead to the same result as by utilizing only the interior point method. In summary, it is shown how the strategic loading is able to minimize the gas emissions and fuel consumption, while being modeled with a high fidelity model as well as a fast computational method, which enabled a combined optimization strategy which is viable to be used in real time. It also provides models that are useful in the design process of hybrid power plants.