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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]

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]

The medium-voltage dc (MVDC) distribution system is a new shipboard power distribution technology that has been extensively discussed and studied by many shipbuilding corporations and ship-owners in recent years. As different types of power converters and ac and dc power distributions simultaneously involved in the system, the system performance for different connections of generators to MVDC converters under varying steady-state operating conditions is essential and important in the design stage of the electrical power distribution system. This type of problem can be analyzed by performing power flow studies. This paper aims presenting a methodology for power flow studies in ship MVDC distribution systems for system planning purpose. A power flow model of the power converters in steady-state is derived to consider medium and low voltage characteristics of electric power system on this type of ship. An ac/dc power flow solution approach then is developed to incorporate ac-system and dc-system models and the ac/dc interface buses in the analysis for determining an appropriate connection of generators and MVDC converters and power converter setting values. Test results of two alternatives for the direct connection of generators to MVDC converters under varying steady-state operating conditions are presented and compared to determine the proper generator-power converter scheme. [ABSTRACT FROM AUTHOR]

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]