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This article presents a robust passivity-based control (PBC) strategy to mitigate the instability effect of the dc–dc boost power converter supplying a constant power load and a constant voltage load in dc microgrid systems. The control robustness of the PBC against both line and load variation is significantly improved by adding the nonlinear disturbance observer (NDO). Using the disturbance estimation technique, this observer works in parallel with the PBC strategy to compensate the disturbances of the system through a feed-forward compensation channel. Based on the dissipation property, the PBC strategy ensures the system stability, whereas the NDO guarantees global trajectory tracking to the reference voltage during disturbances. This control strategy not only ensures large-signal stability of the system, but also provides a fastest recovery performance during disturbances of the system as compared with other PBC strategies. The hardware-in-loop and real-hardware experimental results are provided to verify the control robustness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

In recent years, due to the large spread of power electronics converters onboard shipboard power systems (SPSs), harmonic contamination became an inherent problem. Moreover, as the SPSs are mostly operating in an islanded mode with a limited rating of the generators that feed heavy variable loads, voltage stability issues became a challenge as well. To address these issues, implementing PWM-based FACTS devices using IGBTs such as the active power filters may not be very practical for high-power SPSs due to their limited rated powers, high implementation cost, and high losses. The passive power filters (PPFs) and fixed capacitor–thyristor controlled reactors (FC-TCR) can be effective alternatives due to their capability to operate in high-power applications, smaller losses and, lower cost. The aim of this article is to provide more in-depth analytical investigations to evaluate and compare the behavior of the PPFs and the FC-TCR compensator in reducing the harmonics and enhancing the voltage stability concurrently of high-power SPSs. In addition, details of the voltage stability concept are addressed to visualize the potential risk of the voltage collapse. Besides, the modeling of the FC-TCR and design of the closed-loop control algorithm to ensure voltage stability is conducted. Via intensive simulation studies of a practical ship, which are carried out in MATLAB/Simulink environment, it has been demonstrated that the FC-TCR based on the proposed design can enhance the power quality and voltage stability of SPSs better than traditional PPFs filters. [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]

• Investigating and revealing potential risks of poor energy quality for shipboard microgrids. • Providing a clear view of the importance of selecting the accurate algorithms for analyzing the quality of energy and delivering a comparative study. • Proposing a developed algorithm, which is an offline-based energy quality analyzing technique developed for the short-term protective action stage to assess the energy quality of shipboard microgrids. • Proposing an enhanced algorithm, which is an online-based energy quality assessing technique, Which is very suitable for the long-term preventive action stage. Retrofitting of shipboard microgrids is receiving much attention nowadays due to the flexibility it offers to adapt existing ships with rapid market variations to move towards all-electric ships (A-ESs). This modernity mainly relies on incorporating the power electronics converters that unfortunately draw a large number of harmonics, which affect the energy quality and threaten the system stability and crew/passengers safety. The contribution of this paper lies in proposing two developed open-loop algorithms to assess the harmonics distortion of A-ESs without relying on signal periodicity. The first algorithm is an offline-based analyzing technique developed for the short-term protective action stage, which incorporates the eigenvalue solution inside the short-time fast Fourier transform (ST-FFT) to adapt its window size. Consequently, this algorithm can provide a comprehensive harmonics analysis with a fast transient response even under large system frequency drifts. The second algorithm is an online-based assessing technique, which is very suitable for the long-term preventive action stage to provide accurate harmonics distortion assessment with the fast transient response and efficient computation burden. This approach relies on cascading three moving average filters (MAFs) with particular window sizes to filter and estimate the mean value inside the discrete Fourier transform and the true RMS blocks without the need of frequency information. Hence, it results in enhancing the harmonics rejection capability of the algorithm even under the existence of non-characteristic harmonics and frequency drifts. Simulation and experimental results are provided to validate the efficacy of the proposed algorithms and the results are compared with traditional methods. [ABSTRACT FROM AUTHOR]