In recent years, utilizing the electrical propulsion system in the marine industry has become widely popular. Control of the propeller has been a high-priority design challenge in this industry. One of the essential issues in propeller control is the speed control of the ships. A suitable control strategy for the propeller should be economically-efficient while ensuring stability, reliability, and power quality of the ship's power system. This paper proposes an improved propeller control strategy for increasing/decreasing the ship's speed. This scheme consists of two strategies: a maximum acceleration strategy and an efficient operation strategy. The maximum acceleration strategy aims to quickly reach the final speed setpoint. On the other hand, the efficient operation strategy is deemed to increase the reliability and power quality of the ship power system, as well as having a slightly more acceleration than the conventional method. Moreover, a mechanical index is employed for comparing the performance of the various speed change strategies. By utilizing this index, which is known as loss of life (LoL), the effects of a speed change maneuver on the propeller shaft fatigue are analyzed and the advantage of the proposed method in enhancing the propeller lifespan is discussed. Simulations show that utilizing the proposed speed change scheme decreases the propeller mechanical wear and tear to about 1.8 percent of the conventional methods and consequently will increase its lifespan.
Ship motions affect the propulsion system, which causes fluctuations in the power system. Mutually, the power system variations impact the ship velocity by generating speed changes in the propeller. Therefore, interconnecting the ship hydrodynamic and power system has paramount importance in designing and analysing an all‐electric ship (AES). The lack of an integrated model that can be evaluated in various operating conditions, such as manoeuvring, is evident. This paper explores the required perceptions for the power system and hydrodynamic analysis of an AES. Then, an integrated theoretical model comprising both the ship motion and power system is proposed. In addition to providing an accurate model for the ship in varying situations, this study demonstrates that the ship speed estimation during a ship route change differs from when the interconnections are overlooked. In the light of this determination, a straightforward enhancement for the ship speed control system is proposed. The effects of this modification on the ship power system are explored using the proposed model. The developed model is examined in different scenarios, and its advantages are discussed. It is shown that this model is suitable for employing in the model‐based design of AESs.
Despite the advantages of employing an electric propulsion system in All-Electric Ships (AES), additional power fluctuation sources have emerged in the ship power system as a result. Since the propellers are the primary power consumers in the AES, these fluctuations may significantly affect its power system power quality. Thus, for optimal performance of the ship power system, these fluctuations need to be rigorously investigated at the design level of vessels. Waves collision is one of the critical conditions where propellers inject power fluctuations into the ship power system. Therefore, a comprehensive model is essential to analyze the propellers inand-out-of-water effect on the ship power system thoroughly at the design level. This paper proposes a model-based approach for determining propeller immersion depth variations in collisions with different wave classes. According to this approach, the propellers thrust loss factor caused by the in-andout-of-water effect can be identified. The proposed method is then applied in an integrated AES model. This model interconnects the ship motion and power system dynamics. The in-and-out-of-water impact on the ship power system can be explored precisely in the model-based design of the vessels by utilizing the proposed model. In the end, the proposed method and the interconnected model have been used to simulate a notional ship in a wave collision condition. Simulations demonstrate that the proposed approach can accurately map the substantial impacts of the vessel-wave encountering conditions on the frequency, voltage, and generally on the power quality of the AES power system.
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