In recent years, concerns about severe environmental pollution and fossil fuel consumption has grabbed attention in the transportation industry, particularly in marine vessels. Another key challenge in ships is the fluctuations caused by high dynamic loads. In order to have a higher reliability in shipboard power systems, presently more generators are kept online operating much below their efficient point. Hence, to improve the fuel efficiency of shipboard power systems, the minimum generator operation with N-1 safety can be considered as a simple solution, a tradeoff between fuel economy and reliability. It is based on the fact that the fewer the number of generators that are brought online, the more load is on each generator such that allowing the generators to run on better fuel efficiency region. In all-electric ships, the propulsion and service loads are integrated to a common network in order to attain improved fuel consumption with lesser emissions in contrast to traditional approaches where propulsion and service loads are fed by separate generators. In order to make the shipboard power system more reliable, integration of energy storage system (ESS) is found out to be an effective solution. Energy storage devices, which are currently being used in several applications consist of batteries, ultra-capacitor, flywheel, and fuel cell. Among the batteries, lithium-ion is one of the most used type battery in fully electric zero-emission ferries with the shorter route (around 5 to 10 km). Hybrid energy storage systems (HESSs) are one of the solutions, which can be implemented in high power/energy density applications. In this case, two or more energy storage devices can be hybridized to achieve the benefits from both of them, although it is still a challenge to apply presently such application by a single energy storage device. The aim of this paper is to review several types of energy storage devices that have been extensively used to improve the reliability, fuel consumption, dynamic behavior, and other shortcomings for shipboard power systems. Besides, a summary is conducted to address most of the applied technologies mentioned in the literature with the aim of highlighting the challenges of integrating the ESS in the shipboard microgrids.

Nowadays, the shunt Active power filters (SAPFs) have become a popular solution for power quality issues. A crucial issue in controlling the SAPFs which is highly correlated with their accuracy, flexibility and dynamic behavior, is generating the reference compensating current (RCC). The synchronous reference frame (SRF) approach is widely used for generating the RCC due to its simplicity and computation efficiency. However, the SRF approach needs precise information of the voltage phase which becomes a challenge under adverse grid conditions. A typical solution to answer this need is the application of advanced phase locked loops (PLLs). The PLLs are closed-loop control systems that often have a response time more than two cycles of the nominal frequency.Besides, a special care should be paid in designing their control parameters to ensure their stable operation in all circumstances. This paper proposes an improved open loop strategy which is unconditionally stable and flexible. The proposed method which is based on non-linear least square (NLS) approach, can extract the fundamental voltage and estimates its phase within only half cycle, even in the presence of odd harmonics and dc offset. The performance of the proposed method is verified experimentally and compared with advanced PLLs.

In recent years, the shunt active power filters (SAPFs) have received much attention for compensating the harmonic pollution and also providing the reactive content. A crucial issue in controlling the SAPF is generating the reference compensating current (RCC). Typical approaches for this purpose are using the discrete Fourier transform (DFT) in the frequency domain, or the instantaneous p-q theory and the synchronous reference frame (SRF) in the time domain. The DFT, however, suffers from the picket-fence effect and spectral leakage. On the other hand, the DFT takes at least one cycle of the nominal frequency. The time domain methods show a weakness under voltage distortion, which require prior filtering techniques. The aim of this paper is to present a fast yet effective method for generating the RCC for SAPFs. The proposed method, which is based on the matrix pencil method (MPM), has a fast dynamic response and works well under distorted and unbalanced voltage. Moreover, the proposed method can estimate the voltage phase accurately, this property enables the algorithm to compensate for both power factor (PF) and current unbalance. The effectiveness of the proposed method is verified using simulation and experimental results, and compared with the standard methods.

The shunt active power filters (SAPFs) are broadly utilized to improve the power quality (PQ) issues of electric power systems. A crucial issue in implementing these filters is the accurate estimation of the grid voltage phase/frequency. Indeed, the dynamic behavior and the performance of the SAPF strongly rely on this point. To deal with this challenge, a fast yet effective open-loop synchronization (OLS) technique based on Cascaded Delayed Signal Cancellation (CDSC) is presented in this paper. The proposed technique can reject the odd-order harmonics, the DC offset of the grid voltage, and its dynamic response during transients take an only half cycle of the fundamental frequency. To adapt the proposed OLS technique to the frequency changes, an efficient frequency estimator is also presented. The effectiveness of the proposed OLS technique is demonstrated using simulation and experimental results. INDEX TERMS Cascaded delayed signal cancellation (CDSC) operators, open loop synchronization (OLS)technique, phase and frequency estimators, shunt active power filter.

The increase in greenhouse gas emissions from the transportation sector together with the continued depletion of fossil fuels in general has encouraged an increase in the use of energy storage systems and renewable energy sources at seaports and also on short route yachts and ferries. At present most seaports, particularly smaller ones, are not provided with coldironing facilities -shore based power facilities, which provide electric power to ships from the national grid. Because of the lack of cold-ironing facilities at most ports auxiliary diesel engines and diesel generators on ships must be kept operating and online while at berth to supply auxiliary loads of ship. To address these requirements, one possible solution would be to provide coldironing facilities at all ports. However, in many circumstances, this is not cost-efficient as a port might be far from the national grid. To overcome these limitations a seaport microgrid can be formed through the integration of multiple shipboard microgrids (SMG) with decentralized control together with a charging infrastructure that is located on-shore. This integration of multiple shipboard microgrids and port-based charging stations is termed as a ships-based seaport microgrid. Typically, power is shared among different microgrids using data communication techniques, which adds to the cost and the complexity of the overall system. This paper proposes a communication-less approach based on multi-mode, de-centralized droop control that enables power sharing among several SMGs in both charging and discharging modes based on the state of charge of battery banks -electric power is either supplied or consumed. The proposed approach would be potentially useful for future autonomous ships and also for islands where port electrification is either not technically feasible or an economically viable solution. A simulation and hardware-in-the-loop results are provided to verify the control robustness of the proposed control strategy.