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Offshore oil and gas vessels operating in deep and ultradeep waters demand larger and more sophisticated power and control systems. This tendency brings new system design and integration challenges of the electrical distribution plant especially for platforms requiring marine dynamic positioning and power system redundancy. Voltage stability with continuously changing loads demands and with a limited power generation is essential for islanded integrated power systems, such as the marine systems with increasing presence of power electronic converters to feed variable frequency drives and other electronic equipment. Most of these present a controlled front-end, whose control can affect network voltage with a destabilizing effect. Such a behavior, which is well assessed and studied in traditional land power systems, deserves special attention if the quota of power electronics loads on the total installed power assumes very high values (up to the 85% for new large all electric ships). This work will initially introduce the well-known Constant Power Loads voltage instability issue. Some different system models will be presented, and then will be proposed a methodology to assess the voltage stability at design stage (rather than facing them with equipment retrofits during vessel building or commissioning). Finally, some case study will be discussed, and the solutions to overcome the instability will be presented

Medium Voltage Direct Current (MVDC) distribution is an enabling technology for future large ships, e.g. cruise liners or military vessels. In MVDC systems, shipboard loads are normally fed through power-converters directly connected to the MVDC bus. For such systems a key design goal is voltage stability, impaired by the presence of high-bandwidth controlled loads (Constant Power Loads, CPLs). The paper proposes an approach to stabilize the MVDC bus using the generating systems as sources of stabilizing power. Fast controlled DC/DC converters, interfacing generators to MVDC bus, are employed to control it in a stable way and to provide power sharing among the generators. To this aim, an Active Damping method is exploited. A supplementary Linearization via State Feedback control is utilized to stabilize DC/DC load converters feeding particularly impacting CPLs. Proposed controls are verified by means of time-domain numerical simulations. Shipboard feasibility and performance of the proposed control systems are most considered in the work as conclusions.

Secondary Voltage Regulation (SVR) is part of the hierarchical control system of EHV transmission network, currently operated by the Italian Independent System Operator. SVR is being actuated using automatic voltage and reactive power regulators, named SART, in power stations rated more than 100 MVA. Each SART receives from the Regional Voltage Regulator a reactive level signal and implements it by controlling the reactive power of plant generators, in a balanced way. In this paper, hardware and software architectures of the SART version developed by the authors (NewSART) are presented. NewSART implements control and communication functions using an opensource Real Time Operating System installed on an industrial PC. Such a platform takes advantage of the availability of highlevel development tools and complete communication software libraries. The paper presents the design and principle schemes of the NewSART, along with experimental results of tests carried out during a SVR commissioning campaign.

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All electric ship alternators are connected to a main busbar which feeds all shipboard electric loads. To fulfill power quality requirements of the resulting electrical system, high-performance control of busbar voltage and frequency is needed. Such a task is not of easy accomplishment, due to the complexity of shipboard power station (generators are many and differ by sizes, prime movers, control systems, etc.) and to the intrinsic weakness of the shipboard grid. In this frame, a key power quality issue is voltage control. This paper presents an innovative shipboard voltage and VAR integrated regulator (WIRE). The WIRE controls main busbar voltage and jointly optimizes the reactive power generated by each alternator. It is designed to be interfaced with onboard automation and to realize the integrated management of all reactive power sources (rotating, capacitive, static). Furthermore it satisfies naval requirements as redundancy and fast commissioning

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