Giorgio Sulligoi

Multiconverter Medium Voltage DC Power Systems on Ships: Constant-Power Loads Instability Solution Using Linearization via State Feedback Control

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).

Next-Generation Shipboard DC Power System: Introduction Smart Grid and dc Microgrid Technologies into Maritime Electrical Netowrks

In this article, we examined dc microgrid-based maritime onboard power systems and outlined the need for and potential benefit of employing both smart grid technologies and the MVdc IPS for the future AES to enhance the controllability and efficiency of shipboard power systems. We introduced a series of technical outcomes from research on terrestrial dc microgrids, such as dc power architecture, the application of ESSs, hierarchical control, and different coordination methods. We also presented objective-oriented coordinated management methods and protective functions for future MVdc IPSs, which are to meet the specific need of maritime applications using methodologies from dc microgrids. In the last decade, there were several prototypes of ships on the low-voltage dc level, while, for the MVdc IPS, there are still technological challenges and de-risking studies to be performed. However, it is foreseeable that the advanced technologies from terrestrial dc microgrids are potentially applicable in the MVdc IPS of the future AES. Thus, such a combination will contribute to the implementation of high-performance MVdc IPSs for both commercial and mission-oriented vessels in the near future.

Linearizing control of shipboard multi-machine MVDC power systems feeding Constant Power Loads

Voltage stability in Medium-Voltage DC (MVDC) power systems on ships is a key design goal. MVDC bus voltage stability can be impaired due to the presence of high-bandwidth controlled Constant Power Load (CPL) converters, which can induce negative incremental resistance instabilities. A linearization via state-feedback control is presented in this paper, to stabilize a MVDC bus voltage in presence of destabilizing CPLs. Once a linear control system is obtained, a traditional stable pole placement is operated. The control is designed to be implemented using the controlled DC/DC converters that interface the system power sources to the MVDC bus. The proposed control is verified by means of time-domain numeric simulations based on both an average state space model and a detailed power electronics circuit model, thus providing a two-way comparison.

Power Flow Control and Network Stability in an All-Electric Ship

The concept of an all-electric ship, while offering unprecedented advantages from the point of view of efficiency and flexibility of operation, has introduced new challenges in terms of stability and power flow control. The advent of a full power electronics power system has raised new questions from the point of view of system dynamics, particularly when dealing with the new medium-voltage direct current distribution. The overall goal of guaranteeing a secure operation of the power system has brought researchers to consider two main approaches: reducing the dynamics of the large load to operate in a range of dynamics compatible with traditional generation systems, or making the generator set smarter through its power electronics interface. This paper compares these approaches to stable operation, focusing on the latter considered more in line with the progress of technology and in general more appealing.

Shipboard Power Generation: Design and Development of a Medium-Voltage dc Generation System

This article reports on the design, development, and validation of advanced prototype 2 MVA generation equipment [i.e., naval package (NP)] for a shipboard medium-voltage dc integrated power system (MVDC IPS). The generation equipment is based on an ultrahigh-speed 22,500-r/min 12-phase alternator, which feeds an ac/dc power electronics converter comprising four diode rectifiers and four insulated-gate bipolar transistor (IGBT) choppers. The prototype realization constitutes a follow-up of a previous NP version employing a wound-field 6,300-r/min alternator feeding noncontrolled ac/dc converters. The major technical challenges faced in the design and development of the advanced NP prototype are outlined in this article, taking the previous lower-speed version as a technology reference. The system performance, as determined by the testing campaign, and lessons learned for future studies are addressed.

Modeling, Simulation, and Experimental Validation of a Generation System for Medium-Voltage DC Integrated Power Systems

In this paper, a demonstrative technological implementation of a shipboard 2.15-MVA generation system is described, along with its modeling, numeric simulation, and some factory tests. The system, named Naval Package (NP), is part of a demonstrative program commissioned by Italian Navy for preliminary evaluations of medium-voltage dc supply technologies aimed at equipping its future vessels. The NP is made by a dual-star alternator, whose two stator three-phase windings feed two full-bridge diode rectifiers, respectively. The alternator (rated speed 6300 r/min) is designed to be moved by a 22 000-r/min gas turbine through a gearbox. This paper will present NP innovative issues, with reference to design solutions, operative requirements, dynamic modeling under normal and faulty conditions, and some factory tests.

Improving Power Quality in All Electric Ships Using a Voltage and VAR Integrated Regulator

Power quality is a key issue in island, shipboard integrated electric power systems (IEPS). However, it 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. This paper presents a new approach for controlling voltage and reactive power generated in the power station of an all electric ship (AES). A shipboard voltage and VAr integrated regulator (WIRE) is proposed. The WIRE is aimed at controlling alternators voltage, main busbar voltage and jointly optimizing the reactive power generated by each alternator. WIRE project reunions into an integrated device the most advanced control functions presently implemented in smartest land power stations. WIRE is also endowed with an embedded power-station/IEPS real-time simulator, suitable for performing factory functional, diagnostic and hardware-in-the-loop (HIL) tests. The paper will show how WIRE can improve power quality into an AES, while respecting marine constraints like: reduced room availability, redundancy, reliability, optimal and safe utilization of generators, fast commissioning, diagnostics.

Economical analysis and innovative solutions for grid connected PV plants

The world total photovoltaic (PV) installed capacity is growing very quickly, due to both government incentives and increased environmental concerns. This situation calls for the realization of large, grid-connected ldquoindustrialrdquo PV plants, aimed at delivering energy to the grid. However, the cost/kWh of PV energy is still quite high. This paper reports some of the most promising research approaches currently in progress on new PV materials and devices, focusing on the reduction of PV generation cost expected from the technological implementation of such research. Because of their large size, industrial PV plants could have different characteristics compared to the small ones that, with few exceptions, have been realised until now. This problem is analyzed with the aim of providing a set of recommendations and guidelines for proper design of industrial PV plants, mainly concerning the choice of the power electronic conditioning systems and the use of simulation-aided design tools.

Modeling and Simulation of Electric Propulsion Systems for All-Electric Cruise Liners

Electric propulsion for cruise liners has now become a standard owing to its several advantages. However propulsion drives have a large impact on the ship power system. This gives rise to the requirement for designers to understand in depth the effects of propulsion drives on the ship network in different operating conditions. For this purpose computer simulations have proved to be a very useful tool. In the paper a typical propulsion drive for an all-electric cruise liner is described and simulation results are shown. Owing to the model complexity, simulations turn out to be computationally quite heavy. For this reason a simplified model has been developed. Simulation results, from the ship network viewpoint, proved to be close to the detailed model ones.

The Role of Voltage Controls in Modern All-Electric Ships: Toward the all electric ship.

Ships 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.