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In modern dc shipboard microgrid (SMG) systems, the propulsion motors and hotel loads are always supplied through tightly regulated point of load converters, which behave as constant power loads (CPLs). The negative incremental impedance due to CPL’s characteristics destabilizes the dc bus voltage of dc SMGs. Due to uncertain operating conditions of maritime ships on the sea, the dc bus voltage robust control is a crucial matter. Therefore, this paper presents a cutting-edge systematic review on advanced nonlinear control strategies to stabilize and control the CPLs in dc SMGs, such as sliding mode control, synergetic control, backstepping control, model predictive control, and passivity-based control. The latest stabilization techniques and the future trends towards an adaptive nonlinear control have been presented throughout this review. Several feedforward control-based observation and estimation techniques have been highlighted. The stability analysis and stability challenges of dc SMGs are also discussed. [ABSTRACT FROM AUTHOR]

The penetration of renewable energy is gradually increasing. Therefore, power system flexibility, which is required to maintain system security and to cope with renewable generation uncertainty, becomes more important. Various technologies, such as flexible generators, demand management, energy storage, network reconfiguration, and even efficient system operations, are capable of improving power system flexibility. Nevertheless, among them, flexible generation resources can provide a direct way to enhance the power system flexibility. This article first applies the fuzzy analytic hierarchy process to calculate the flexibility index of generation resources. Then, the process of unit scheduling is implemented under various operation scenarios to investigate the relationship between the generation flexibility and the cost of unit scheduling. Finally, the required flexibility and the corresponding capacity of flexible generators under a specified penetration of renewable power generation are investigated under different operation scenarios. [ABSTRACT FROM AUTHOR]

Seaports are specifically designed for trading purposes. They are equipped with facilities for handling industrial and commercial goods as well as raw materials stored in containers. These facilities are often based on diesel cranes, which are noisy and produce air pollution. A possible solution to address this problem is replacing the diesel-power cranes with the electric ones. This idea, however, demands a high power connection to the grid in the seaport. This paper presents a cost-effective and environmentally friendly solution based on an electrical flywheel system to reduce electricity consumption from the electrical power network while improving system efficiency by using already existing technologies. Besides, this study presents a new method for controlling electrical drives using flywheel energy storage systems in harbor crane applications by exploiting the energy harvested from the cranes. The system model, including the electrical grid, cranes, power electronic drives, and flywheels as energy storages, is presented and an effective control methodology is developed. Simulation results of a practical crane system are presented and discussed. Practical lab-scale setup is also built and tested. The results have shown that by using the proposed method, the energy can be effectively harvested from the crane into the flywheel energy storage system during its operation, which significantly enhances the harbor power system efficiency as well as supply quality. [ABSTRACT FROM AUTHOR]

Power quality (PQ) is becoming more and more critical issue in shipboard microgrid systems (SMGs). Especially, the impact of voltage unbalance combined with harmonic distortions on the SMG behavior has not been fully investigated. In this paper, simple PQ assessment models and a series of controlled experiments are proposed and carried out in a real ship under sea-going conditions. The ship experimental results are presented and discussed considering nonlinear bow thruster load and high power ballast pump loads under unbalanced and harmonic voltage conditions. In addition, the analysis of bow thruster current harmonic surges during the ballast pump start-up is presented. Furthermore, the voltage/current distortions of a working generator, bow thruster and pump loads are analyzed. The paper provides a valuable analysis for coping with PQ issues in the SMG. [ABSTRACT FROM AUTHOR]

One of the most basic tasks for ship power system design is electrical load analysis, which is used to determine the required installed capacity of on-board power generators. Traditionally, the analysis is carried out based on considerations of investment cost and supply adequacy, while using a design of generators with the same rating. It does not consider the energy efficiency, thereby in some cases resulting in the generators operated at a lower efficiency under heavy loading conditions and high energy consumption. To enhance power generation efficiency and reduce energy cost, a new load analysis method for marine vessels is proposed in this paper. The relationship of operating efficiency and load factor of generators is mathematically modeled and considered in the analysis. The problem is formulated as a nondifferential combinational optimization problem, where the total generation cost during a whole voyage is minimized subject to system operation and technical constraints, in order to derive the optimal generator rated power and unit commitment using genetic algorithms. The results confirmed the validity of the proposed method through load analysis of a practical ship power system, as well as energy-saving benefits using the proper generator rated power and an accurate load model for power pumps. [ABSTRACT FROM AUTHOR]

A multiagent-based feeder automation system is developed for the service restoration of power systems in a navy ship after fault contingencies. In the system, power-electronic-building-block agents of the multiagent system (MAS) are used to derive the proper restoration plan after the faulted location is identified and isolated. To assure that the restoration plan complies with operation regulation, heuristic rules based on standard operation procedures of the shipboard power system (SPS) are included in the best first search of the MAS. Two control schemes for SPS restoration are investigated, and their performances are evaluated and compared using a discrete event simulation technique with respect to restoration time. For fault contingency when the capacity reserves of supporting feeders are not enough to cover the fault restoration, the load shedding strategy is derived for the MAS to restore service power to as many key loads as possible. A navy SPS with 72 feeders is selected for computer simulation to demonstrate the effectiveness of the proposed methodology. The study concludes that, to cover feeder automation functions, a MAS with distributed processing capability provides better reliability performance than the centralized control. [ABSTRACT FROM PUBLISHER]

A poor power factor is often overlooked in ship power systems where electric motors are widely used to drive a variety of machinery and operate numerous processes. By reducing the reactive power produced by power generators through power factor correction (PFC), not only have system operating efficiency and economic targets been enhanced but greenhouse gas emissions have been also reduced. An evaluation of the economics of power factor improvement should take into account diesel electric generator loading, fuel oil consumption rate, running time, operating efficiency, and the production of emissions. This will help achieve energy-saving evaluation and ensure that the additional capital costs of installing a PFC system will provide an adequate rate of return on investment. This paper presents the methodology and results for the economic evaluation of PFC in marine vessels. A mathematical model, used to determine the relationships among fuel oil consumption, emission, and power factor for the diesel electric generator, is derived to quantify the possible benefits with PFC. An economic evaluation method using present worth analysis is performed to evaluate the PFC system. Numerical analysis and field test of practical ship power systems confirm the validity of the proposed approach and the critical parameters for PFC economics are determined. [ABSTRACT FROM PUBLISHER]

Induction motors are widely used in ship electrical power applications as they are frequently switched on into the supply system, consuming about 70% of the electrical energy generated. Voltage sag, which is produced by the starting current of induction motors, is one of the main causes of sensitive equipment dropout and, as such, must be considered in ship electrical system designs to comply with classification societies' rules. A simple and fast method that is able to estimate the expected magnitude of voltage sag disturbances and provide information about the effectiveness of the various mitigation methods is essential. This paper aims at presenting a faster evaluation method for voltage sags due to motor start-ups in ship electrical power systems. The performance of the proposed method is validated by measurements gathered from several motor starter designs in practical ship power applications using the Riemann-summation-principle-based evaluation method. The proposed method can provide engineers with useful information about the actual magnitude of sag disturbances as well as on the effectiveness of motor starters for ship electrical power applications, which will assist them in determining proper motor starter designs. [ABSTRACT FROM AUTHOR]