Integrated power systems are popular in the shipbuilding industry. DC shipboard microgrids (dc-SMGs) have many advantages compared with ac ones in terms of system efficiency, operation flexibility, component size, and fault protection performance. Being in the exploring stage, dc-SMGs have several potential configurations with different system architectures and voltage levels. In a dc-SMG, functional blocks integrated include power generation modules (PGMs), propulsion system, high power loads, and pulsed loads specifically in naval ships. In modern ships, the PGMs include not only generators and fuel cells but also energy storage systems (ESSs), which cooperate with generators to improve the overall efficiency and reliability. High power electric converters are vital interfaces between the functional blocks and the dc distribution system. Rectifiers for generators take the tasks of dc bus voltage regulation and power sharing. Inverters for propulsion motors are responsible for the motor drive in different operating conditions. Bidirectional dc/dc converters for ESSs are used to provide supply-demand balance and voltage fluctuation mitigation. This article makes a comprehensive review of power architecture, functional blocks including electrical machines and energy storage, as well as power converters in dc shipboard power systems.

This article presents a review of coordinated control strategies, stability analysis, and fault management for dc shipboard microgrids (dc-SMGs). As an emerging application, the dc-SMG lacks a comprehensive summary of the control schemes. Considering the specific load profile in ships, this article discusses the coordinated control strategies of diesel generators and energy storage system. Depending on the maritime conditions, different operation modes are switched by the energy management system. Due to the presence of high-bandwidth controlled constant power load converters, negative impedance instability is induced. Meanwhile, the pulsed loads in dc-SMG may affect the voltage stability significantly. Small-signal and large-signal stability analysis can be used to evaluate the effect of these two types of loads. In the aspect of the shipboard protection system, this article presents the specific requirements of dc-SMG based on the standards. Lacking “ground” in ships, solutions in designing the grounding system for dc-SMG is described. Besides, the short-circuit fault management consisting of fault detection, fault isolation, and reconfiguration in dc-SMGs are summarized. Finally, the existing commercial dc ships are presented and compared to demonstrate the developing trends.

The virtual synchronous generator (VSG) control has been extensively applied for realizing grid-friendly interconnections of power converters. Nevertheless, due to the direct shaft dynamics emulation, low-frequency power oscillations may be introduced in the case of limited damping effects. To solve this issue, power control law modifications have been proposed based on the feedback control theory. Although power oscillations can be suppressed to an acceptable level, the original inertial response of the VSG will be significantly degraded. This letter proposes a new damping method based on the reference feedforward control. The proposed method is able to effectively attenuate poorly damped power oscillations in VSG-controlled converters without affecting the original inertial response. Theoretical analysis and effectiveness of the proposed damping method have been validated by both electromagnetic transient simulations and experiments.

Hybrid electric ships powered by diesel generators and batteries are the main configuration for shipboard microgrids (SMGs) in the current maritime industry. Extensive studies have been conducted for the hybrid operation mode, whereas the all-electric operation mode and the switching between the aforementioned two modes in a system with multiple generators and batteries have not been tested. In this paper, a coordinated approach for a hybrid electric ship is proposed, where two operation modes have been simultaneously considered. More specifically, for achieving an efficient operation with reduced generator wear losses, the governor-less diesel-engine-driven generators have been adopted in the study. According to the practical operation conditions, two operation modes, the all-electric and hybrid modes, are preset. Based on these, the coordination of the generators acting as the main power sources and batteries regulating the power flow and improving the generator efficiency is studied. The governor-less diesel generators are regulated to inject the rated power in order to maximize the generator efficiency, while the DC bus voltage is regulated by DC/DC converters. For the benefit of the overall lifespan of battery banks, power sharing during charging and discharging states have been realized by the state of charge (SoC)-based adaptive droop regulator. For the test of two operation modes, as well as the mode switching, a simulation assessment in a 1 kV DC SMG has been conducted. The simulation results show that the DC bus voltage can be controlled well, and that the power sharing among batteries follows the design. Additionally, smooth transients can be observed during mode switching when the proposed control scheme is applied.

In this paper, we propose and experimentally demonstrate a rate-adaptive multiple-input-single-output (MISO) visible light communication (VLC) system, realized by superposition coded modulation (SCM) with hybrid geometric-probabilistic shaping (GPS). This approach ensures fine-grained net data rate (NDR) per user with flexibility, while simultaneously enhancing the overall NDR performance for all users. We design a hybrid GPS strategy for the proposed rate-adaptive MISO VLC system, which is robust to non-ideal factors such as high channel correlation, nonlinearity, and power competition, and is also insensitive to variations in the probabilistic shaping (PS) factor. Additionally, we propose a universal method for determining the optimal geometric shaping factor. A comprehensive experimental study of the proposed SCM-based hybrid GPS rate-adaptive MISO VLC system is conducted and compared with traditional rate-adaptive single-input-single-output (SISO) VLC systems. Experimental results demonstrate that the proposed system enhances the NDR by 19% for the near-end user and 105% for the far-end user compared to the rate-adaptive SISO VLC system with the PS quadrature amplitude modulation (QAM) signal. Furthermore, compared to the rate-adaptive SISO VLC system with the regular QAM signal, the proposed system not only significantly increases the NDR but also extends the maximum transmission distance by 111.1% under an NDR constraint of 30 Mbps.

Actively commutated current source converter based high-voltage direct current transmission (CSC-HVDC) with state-of-the-art high power IGCTs is a promising candidate due to its merits such as fault ride-through capability and small footprint. The existing dc fault models of CSC either focus on 3-level CSC topology or neglect the transient process and commutation of the converter after fault, not suitable for accurate dc fault analysis of CSC-HVDC. Moreover, the elimination of ac-filters at the point of common coupling (PCC) will lead to severe PCC voltage distortion of weak-grid connected CSC-HVDC after fault. The interaction between the valve-groups caused by the voltage distortion and its influence on the fault characteristics is yet to be studied. In this article, two dc fault analysis models for CSC-HVDC connected to ac grid with different strengths are proposed. Based on quasi-steady state assumptions and substitution theorem, a simplified model by decoupling the valve-groups at the PCC and its adaptability under different grid strengths are proposed for analytical studies of dc fault. For weak-grid connected CSC-HVDC, a fault analysis model is further derived based on the quantitative analysis of the interaction between valve-groups. The proposed models are validated through PSCAD simulations and HIL experiments.