Generally, ships use a three-phase power system with low-voltage and ungrounded systems to ensure continuous power supply. In these shipboard power systems, ground faults constitute approximately 95% of all faults. Most ground faults are due to the single line-to-ground fault. Ground faults can cause blackouts, which significantly impact the safe operation of ships. Therefore, ship engineers should identify the ground-fault region for effective management and resolution. This study analyzed the variations in the phase-to-ground voltage and neutral-point voltage during a ground fault in a distribution network of an ungrounded low-voltage ship. We proposed a practical method for ship engineers to determine the ground-fault phase by measuring only the phase-to-ground voltages. To verify the applicability of the practical method to real ships, the line-to-ground capacitance was directly measured for a 225 V power system of a training ship. Moreover, we performed simulations based on the measurement data and analyzed the variation characteristics of the phase-to-ground voltage and neutral-point voltage during a single line-to-ground fault. Thus, ship engineers can use the simulation results and proposed table to accurately determine ground faults by measuring only the phase-to-ground voltages.

Gas turbine engines at sea, characterized by nonlinear behavior and parameter variations due to dynamic marine environments, pose challenges for precise speed control. The focus of this study was a COGAG system with four LM-2500 gas turbines. A third-order model with time delay was derived at three operating points using commissioning data to capture the engines’ inherent characteristics. The cascade controller design employs a real-coded genetic algorithm–PID (R-PID) controller, optimizing PID parameters for each model. Simulations revealed that the R-PID controllers, optimized for robustness, show Nyquist path stability, maintaining the furthest distance from the critical point (−1, j0). The smallest sensitivity function $Ms$ (maximum sensitivity) values and minimal changes in $Ms$ for uncertain plants confirm robustness against uncertainties. Comparing transient responses, the R-PID controller outperforms traditional methods like IMC and Sadeghi in total variation in control input, settling time, overshoot, and ITAE, despite a slightly slower rise time. However, controllers designed for specific operating points show decreased performance when applied beyond those points, with increased rise time, settling time, and overshoot, highlighting the need for operating-point-specific designs to ensure optimal performance. This research underscores the importance of tailored controller design for effective gas turbine engine management in marine applications.

As the regulation of exhaust gas emitted from ships has been strengthened and maritime autonomous surface ship has become a global issue, electrical propulsion ships that use high voltage and are easy to maintain are in the spotlight. In addition, according to the Eco-Friendly Vessel Act, new government-run ships will be built with electrical propulsion system. Because this system is unfamiliar to the existing seamen, ship managers, and those related to autonomous ships, it is essential to develop a training course. Since the AC drive(power conversion device) is the most important device, the contents of training model should focus on the operation and maintenance of this device. For this, first we review domestic and foreign laws, regulations including the STCW convention, IMO model course and manufacturer"s training course. Finally, in this paper, we propose a AC drive training model and contents for high voltage electrical propulsion ships.

다양한 해상환경에서 운용되는 해군 함정의 가스터빈 엔진은 안정적인 속도 제어가 중요하다. 이를 위해서는 엔진 특성을 반영한 정밀한 수학적 모델링과 제어기 설계가 필요하다. 따라서 본 연구에서는 해군 함정에서 많이 사용하는 LM-2500 엔진에 대해 실제 함정의 시운전 자료를 활용하여 3개의 동작점에 대해 3차 선형모델인 공칭 플랜트를 유도한다. 그리고 제어기 설계를 위해 공칭 플랜트는 1차 시간지연 모델로 근사화하고, IMC 기법과 선형 PID 제어기를 결합하여 속도 제어를 위한 IMC-LPID 제어기를 제안한다. 이 제어기는 필터 시정수 조정만으로 PID 제어기의 파라미터를 결정할 수 있어 동조가 편리하다. 제안한 제어기는 공칭 플랜트와 파라미터가 변동한 불확실성 플랜트에 적용하고, 시뮬레이션을 시행하여 추종 및 외란 억제성능, 강인성을 정량적으로 평가한다. 시뮬레이션 결과 제안한 제어기는 추종 및 외란 억제성능 모두에서 우수한 성능을 나타내었다. 특히, 실제 가스터빈 엔진의 운용 환경인 파라미터 변동을 고려한 불확실성 플랜트에 대해서도 우수한 성능을 보여 실제 제어기 설계에서도 하나의 방법론으로 기여할 것으로 기대된다.