Bus voltage stability is a key issue in future medium-voltage DC (MVDC) power systems on ships. The presence of high-bandwidth controlled load converters (Constant Power Load, CPL) may induce voltage instabilities. A control design procedure is presented which starts at the modeling level and comes to control implementation. A control method based on a Linearization via State Feedback (LSF), is proposed to face the CPL destabilizing effect and to ensure the MVDC bus voltage stability. A multiconverter shipboard DC grid is analyzed by means of a new comprehensive model, which is able to capture the overall behavior in a second-order nonlinear differential equation. Exploiting DC-DC converters that interface power sources to the bus, LSF technique is able to compensate for system nonlinearities, obtaining a linear system. Then, traditional linear control techniques can be applied to obtain a desired pole placement. With reference to system parameters mismatch, LSF control design is verified by means of a sensitivity analysis, evaluating the possibility of an over-linearization strategy. Time-domain numerical simulations are used to validate the proposed control, in presence of relevant perturbations by means of a two-way comparison (average value model and detailed switching model)

hips have witnessed an astounding evolution in the last 200 years. the introduction of the combustion engine has started an ever-faster change, both in the performance and functionality given by the ships. From the steam-powered ships of the early 1800s to the modern diesel-electric ships, the improvements were significant and increasingly rapid. in particular, in the last 30 years, the design of ships has made a huge leap ahead, both in terms of efficiency of the entire vessel and new functions given to the owners. this is due to the progressive electrification that has occurred. almost a century ago, at the time of the birth of the modern ship propulsion, the competition between electrical drives and the then-growing mechanical drives was strong.

This paper deals with voltage stability of DC power systems in More Electric Vehicles (MEVs) in presence of Constant Power Loads (CPLs). Large signal voltage stability is studied according to Lyapunov theory. Original analytical developments are presented to evaluate a Region of Asymptotic Stability (RAS) around a system's stable equilibrium point. Analytical forms are found, which show how the RAS boundaries vary as a function of the system's supply voltage, when the latter is floating. The validation has been carried out by means of the numerical continuation analysis. This result makes it possible to point out how supply voltage fluctuations can decrease the RAS, up to impairing voltage stability not only for large, but even in case of small perturbations

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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.

Voltage control represents one of the main challenges in the development of Medium Voltage DC power systems on ships. The presence of non-linear loads (high-bandwidth controlled converters, CPLs) may cause dangerous voltage oscillations or even instability in presence of small or large disturbances (e.g. connection/disconnection of loads). To face this important issue, the voltage actuator approach appears as an effective solution by using DC/DC converters as sources of stabilizing power. Such controlling action is obtained by imposing control signals determined by different techniques. In this regard, the main goal of this paper is to analyze the action of three control techniques (State Feedback, Active Damping and Linearization via State Feedback) in order to suggest the implementation considering the system criticality (e.g. the CPL power or the filter damping factor). Numerical simulations are useful to compare the proposed methods by observing the control action in presence of growing disturbances

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In shipboard DC grids, tightly controlled load converters can impair the system stability, thus provoking the ship blackout. Conversely, load converters regulated by low control bandwidths are capable of inducing a stabilizing action. This compensation is verifiable if the loads are few. On the contrary, the balancing of control dynamics is hardly evaluated if the bus feeds multiple (i.e., hundreds or more) DC controlled loads. In this paper, the weighted bandwidth method (WBM) is presented to assess the small-signal stability of a complex shipboard power system by aggregating the multiple converters into two sets of controlled loads. Once the validity of the aggregation is proven, a stability study is performed on the two-loads system. As the last system is more inclined to instability than the initial multiple-loads system, the verification of the two-loads stability criterion guarantees that the shipboard DC grid also remains stable. Finally, emulations on HIL verify the proposed stability assessment thus providing the first unique verification of WBM.