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Over the past decades, the growth of international cruise tourism has been constant. The forecasts made by the Ships and Maritime Equipment Association indicates an annual growth rate of about 7%, leading to the triplication of global cruise passengers in the future (from 19 million passengers in 2010 to more than 54 million in 2035). To cover the future market needs, roughly six or eight new cruise ship buildings per year are planned until 2031, along with an increase in ship size (up to 8,000 persons accommodated onboard). These two facts have led to a growing interest in the passengers' safety, which has been addressed by the International Maritime Organization (IMO) Maritime Safety Committee (MSC) in 2000, with the launch of an initiative for adequate international safety regulation for large passenger ships. The first issue that emerged from such an initiative was the difficulty in safely evacuating passengers toward lifeboats during emergencies (in particular, during a fire or flooding). The solution proposed by the MSC requires that future passenger ships be designed to increase their intrinsic survivability, exploiting the concept that the ship is its own best lifeboat (thus avoiding abandoning the ship as much as possible). Such a solution was formalized in December 2006 through a package of amendments to regulations dedicated to large passenger ships and published in the 82nd session of the MSC, i.e., the Resolution MSC.216(82), commonly known as safe return to port regulations (SRtP).

Load commutated inverters (LCIs) are still widely used for their robustness and reliability in high-power synchronous motor drives, in either single or multiple three-phase configurations. A restriction to their use in high-speed applications is due to the criticalities of thyristor operation at high switching frequencies. The upper frequency limits of LCIs are usually addressed in the existing literature as something independent of the drive architecture. On the contrary, this paper highlights how the maximum frequency that can be safely attained closely relates to the number of LCIs that are used to supply the synchronous motor. In fact, moving from a single to multiple three-phase arrangements is proved to introduce more stringent frequency constraints due to the mutual interaction between stator windings during commutations. Frequency limits for safe operation of single- and multiple-LCI drives are derived in quantitative terms and experimentally assessed on a 2-MW synchronous motor fed by a couple of LCIs. Practical implications of such limits in the design of high-power high-speed drives are finally discussed.

The paper deals with the reactive power compensation in single-phase systems by active power line conditioners (APLCs), focusing on the effectiveness of the compensating action when the utility voltage is distorted. The existing compensation approach, based on the achievement of a sinusoidal load current, is first presented, showing that it suffers from some shortcomings. A novel compensation approach, based on the achievement of a unity power factor, is then proposed that has the merit of overcoming the shortcomings of the existing one and, in addition, of outperforming it in terms of power delivery capabilities of the utility. Effectiveness of the proposed compensation approach is corroborated by simulation results.

Electrical propulsion is not a novel concept in marine systems. However, the availability of power electronic converters has proved to be the Key Enabling Technology for electrification of large ships. This paper starts with a summary of EP drives, which led to the birth of all-electric ships. Electric power generation and control systems are then presented, which make it possible to exploit the integrated electrical power system. To ease comprehension of the issues in designing such a system, its conventional design process is given. Then, the reasons that are pushing ahead the research in the shipboard power systems sector are discussed. The need for research in the design methods area is demonstrated through an overview of the latest results of technological research. Finally, a summary of the most significant results on the design tools research is given, including early stage design, dependable-oriented design, and the improvements achievable through software simulators and hardware-in-the-loop are discussed. The goal of this paper is to demonstrate why research on design methods is as important as a technological one, on the basis of the needs concerning the design, integration, and management of future “integrated electrical and electronic power systems” (power systems with power conversion quota approaching 100%).

Nowadays, the Medium Voltage Direct Current (MVDC) technology represents a new possibility to renew the shipboard power system of large All Electric Ships (e.g. cruise liners or military vessels.). This new concept is capable of achieving valued advantages, such as simplified system integration, modularity and system efficiency, together with an expected reduction of the space devoted to technical system. For a shipyard interested in keeping a leading position in the market, such benefits will be the main strength points. Therefore, the MVDC Large Ship research program (presented in the paper) has been carried out trying to meet with the industrial needs of one of the partners, whose expertise deeply influenced the research and was deemed indispensable: Fincantieri Shipyard.

Dependability has only recently become a unified theory, developing its own taxonomy, lexicon and methods. This newly formed discipline now regroups concepts defined and developed within international rules corpus in different areas of engineering, such as: aerospace, automotive, computing, etc. Applications to marine sector are, at present, partial, lacking in terms of systematic approach and limited in extension. Dependability techniques provide system analysis methods that classify faults, detail consequences with associated risk index. These indications are quintessential in assessing design progress and effectiveness, in discussing issues and consequent modifications required, in quantifying impact of faults in terms of operations, in directing product and documentation development, rendering easier and less conflictual demonstrating specification adherence. Aim of this work is demonstrating dependable design can be obtained with a bearable effort, implanting dependability techniques on an already present ship design substrate, and that dependability techniques may be profitably employed as project management tools.

DC distribution is being considered as an attractive alternative to its traditional AC counterpart in many fields of applications and, in particular, for shipboard power systems. The adoption of a DC distribution network makes it possible and sometimes necessary to radically revise the technology of the generation systems in many regards. Not only frequency-related constraints are removed, allowing for high-speed smaller generators to be used, but new fault-tolerant configurations, involving power electronics, generation control and management too, become feasible as a natural alternative to the traditional arrangement of AC power plants. In this paper some of these new technological scenarios are outlined, referring to state-of-the-art realizations as well as to novel concept designs presently under development and investigation.

Integrated Power Systems (IPS) with DC distribution require the massive use of power electronics for many tasks: 1) the output voltage rectification of generators and the connection of energy storage systems to the IPS, 2) the supply of medium voltage high power users (propulsion drives, bow thrusters, compressors for air conditioning), 3) the adjustment of voltage levels, which is performed by power transformers in AC distribution systems and by DC/DC power converters called Solid-State Transformers (SST) in DC distribution systems. In this paper, an overview is given of the power converters found in the literature and on the market that could be suitable for employment in the mentioned subsystems as parts of a future MVDC IPS. Finally authors propose a structure for an SST to be employed in three-wire MVDC power systems.

A promising solution to improve tomorrow's all-electric ship onboard power system design and performance relies on moving from 50-Hz or 60-Hz AC distribution to a Medium-Voltage DC (MVDC) grid. This paper provides a review of presently-available and under-development technologies for electric generators to be used in perspective MVDC shipboard systems. The inspiring reason for the survey lies in the fact that an MVDC grid design removes the constraints usually imposed on shipboard generation group design and opens the way for a wide variety of non-conventional machine alternatives. In combination of high-speed gas turbines, that can be employed as prime movers, several electric machine topologies, not yet used for ship applications, can be selected to feed MVDC onboard systems. Along with a review of possible generator types suitable for such use, the paper critically reviews some emerging technologies for their fault-tolerance enhancement through conventional and innovative split-phase architectures.

The degree of complexity of Integrated Power Systems (IPS) for All Electric Ships (AESs) points out the need to review the design process from a dependability perspective. This paper suggests the application of dependability concepts and definitions to accomplish to requirements set by recent rules and regulations in the field of threat levels for shipboard electrical equipment. Guidelines about 1) how to properly decompose the IPS into conceptual subsystems and 2) how to apply to analyze them, using the Fault Tree Analysis (FTA) and the Failure Mode and Effect Analysis (FMEA) are presented and discussed. As a case study, the IPS of a new built large AES is chosen.

Vehicular traction motors are usually designed to operate over a wide speed range and require important flux weakening capabilities at high speeds. This paper presents and innovative design intended to endow an interior permanent magnet (IPM) motor with an intrinsic capability of reducing its own rotor flux at high speeds. The design does not involve any additional current source nor control systems for rotor flux regulation. It relies on a purely mechanical device that establishes a partial magnetic short circuit between rotor permanent magnets. The device is able to self-activate due to centrifugal force when the speed exceeds a given threshold that can be fixed by the designer. The design features of the proposed IPM motor are illustrated in the paper and its static and dynamic performance prediction through finite element analysis (FEA) methods is presented. A prototype construction is presently in progress to experimentally validate the solution.

Permanent-magnet synchronous motors are widely used in vehicular traction applications due to their high efficiency and torque density. A critical point of their operation is the flux weakening needed at high speed, which usually implies injecting a d-axis demagnetizing current by the inverter. This paper presents a critical survey of the alternative approaches found in the literature and patent databases to enhance flux-weakening performance by acting on motor mechanical and electromagnetic design.

DC distribution is an attractive solution for onboard integrated power systems of new-generation all-electric ships, especially thanks to the benefits it offers in terms of reducing generation system size, weight and power consumption. Technologies have already been implemented in full-scale prototypes based on synchronous generators feeding the DC grid through rectifiers. In these proven solutions, the voltage control is allocated either to the generator excitation system or to the rectifier control. This paper investigates a design variant where both voltage control loops exist and act simultaneously. The basic design of the system is presented along with its modeling in the Matlab/Simulink environment. Simulation results obtained from the Simulink models are finally reported illustrating the system behavior during various electrical and electromechanical transients. (6 pages)

The paper deals with the dependability theory and the functional safety standards. Dependability is concerned with the ability of a system to deliver the intended service, including the ability to cope with a fault. Functional safety is concerned with the safety-critical systems and focuses on the characteristics of the extra systems added to a system with the purpose of making its operation safe. The paper starts by providing the definitions of system and service. Then the key concepts of the dependability theory are presented, which are the threatens, the attributes and the enforcing techniques. Particular attention is given to the fault-tolerance techniques and the architectures of the fault-tolerant systems. Afterwards the key concepts of the functional safety standards are presented, which are the hazard and risk analyses of a safety-critical system and the safety requirements for the extra systems. At last, two study cases represented by industrial electronics systems are examined from the standpoint of both the dependability and the functional safety.

Nominal voltage of the traction motors being used in electric vehicles is typically higher than the voltage generated by the onboard DC sources. Thus, motors of AC type require boost as well as inversion of available DC voltage. This can be done either by a DC-DC boosted inverter (DBI) or by the recently introduced Z-source inverter (ZSI). Since drives with PM brushless DC (BLDC) motor are largely utilized in the traction of light electric vehicles, it is of interest to carry out a comparative analysis of the two supplies when feeding such kind of motor. In this paper, DBI and ZSI supplies are designed for the study case of an electric city scooter propelled by a PM BLDC motor and powered by a fuel cell with the assistance of a battery. Ratings of the transistors and sizes of the passive components for the two supplies are determined as a function of the fraction of the fuel cell power to the nominal power of the traction motor. The design results are discussed.

The paper presents the activities ongoing in the framework of a two-year Italian National Research Project aimed at developing a distributed Driving and Steering (DaS) system for Electric Vehicles (EVs). The system is built up around an actuation module embedding a rotary-linear motor and including a power converter and a local Electronic Control Unit (ECU) to supply and control the motor. The actuation module is intended to make a wheel active so as to give it propelling and steering capabilities. The DaS system, in turn, includes a central ECU and a fieldbus to govern and network the system, and a power supply stage. The Project under consideration is focused on a DaS system with two active wheels for a light-duty EV.

The paper presents a small-signal stability analysis of voltage control systems employed onboard all-electric cruise liners. To realize the stability analysis, a model of shipboard power station voltage control system has been determined, moving from dynamic models of alternators, voltage regulators and loads. Reduced order models of alternators have been utilized, to simplify at best the analysis. Analysis results have been validated through numerical simulations, using a simulator of power station electromechanic quantities developed at the University of Trieste. Such simulator includes alternators, voltage and frequency regulators, breakers, protections and R-L loads. Numerical results obtained from simulations of both complete and reduced order models fully validate the analytical findings, while computation times are in the order of real-time simulations.

A simple fault-tolerant induction motor drive with v/f speed control included in the electrical auxiliary equipment of railway locomotives is presented in the paper. The employment of fault tolerant on-board electrical auxiliary equipment increases the dependability and then the quality of the railway service. The fault tolerance technique consists of some emergency countermeasures applied in case of fault. It includes a fault diagnosis procedure based on the analysis of the current vector, the connection of the stator winding neutral point to the dc-link middle point and the variation of the v/f law, taking into account the contribution of the zero-sequence impedance and the need for a flux weakening in order to avoid saturation. Some experimental results are reported showing the improved performance of the motor drive under fault conditions by means of the proposed remedial strategy.

RTAI extension to Linux operating system makes it possible to perform Hard Real-Time (HRT) controls using a commercial PC and utilizing open-source code. This paper details a software installation process, along with the suitable hardware chosen for realizing motion controls using Linux-RTAI. Advantages offered by the possibility of designing and developing motion controls using the powerful tools of high level object-languages (i.e. Simulink) are described. It is proven that the combination of Simulink as a development environment and Linux-RTAI PC as a controller platform brings advantages that can be greatly appreciated in industrial motion control applications, such as: very reduced time for development, diagnostics, design of controls; adequate control performance; cost reductions offered by the open-source status of the operating system.

The paper deals with a direct torque control (DTC) scheme for Induction Motor (IM) drives where flux and torque of the motor are estimated by the IM current model instead of by the voltage model. The scheme is intended to enable operation of the DTC IM drives at zero speed. As a return, its implementation requires the knowledge of speed, rotor time constant and inductive parameters of the motor. In the paper the performance of the proposed scheme is studied for a drive equipped with an incremental encoder and commanded with a constant flux. Using the position information delivered by the encoder, a suitable representation of the current model is formulated that makes the drive operation feasible at true zero speed. Operating with a constant flux command, the variations in the rotor time constant dominate over the other parameters; their effect on the drive behavior is analyzed in steady state founding that the motor flux and torque are deviated from the references of a quantity, which is a function of the torque reference. Experimental results are given to substantiate both the capabilities of the scheme of developing the full torque at a standstill and the theoretical findings on the drive behavior under rotor time constant mismatch.

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.

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.

Dependability and safety of a system are topical subjects, which have found the proper assessment in two formal corpuses: the dependability theory and the functional safety standards. The purpose of this paper is to explicate the two corpuses, showing how one corpus supplements the other one. At first the dependability theory is introduced and the related concepts of threatens, attributes and techniques are presented. Regarding the safety, the dependability theory limits itself to the enunciation of principles and axioms without giving considerations to the problems of their applications to an industrial system. This gap is filled up by the standards on the functional safety, which are introduced in the second part of the paper together with the concepts of risk, safety function and safety integrity level. Finally, as a case of study, the power converter supplying the air brake system aboard train is examined from the dependability and functional safety viewpoints.

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.

Steer-by-wire (SbW) systems are candidate to replace the conventional steering equipment in the new generation of vehicles. The task of a SbW system is twofold: turning the steered wheels by tracking the handwheel rotation and providing the driver with a feeling of the steering effort. In this paper, the design of the control scheme for SbW systems is faced. Two schemes are considered: one is derived from the model of conventional steering equipment whilst the other one exploits the features of a SbW system to cope with the interaction of the steered wheels to the road surface. Implementation of the control schemes on a test vehicle is described and experimental results are given.

This paper is concerned with the self-commissioning of rotor-flux-oriented (RFO) induction motor (IM) drives operating at variable flux. A solution is proposed which identifies the magnetization characteristic of the motor by means of one test only. During the test, the motor is kept at standstill with a single-axis supply. Within the same test, the rotor resistance is also identified. The solution is suitable to be implemented in commercial drives, as it makes use of the on-board hardware. The paper starts by reviewing the model of a saturated IM under single-axis excitation. Then the theoretical bases of the solution are set forth and the test is formulated. Afterward, an experimental rig is built around a commercial RFO IM drive and the magnetization characteristic of the motor is identified. Its comparison with data obtained from standard no-load tests with different voltage supplies confirms the validity of the solution.

AC machines have become the industrial standard not only in high power-constant speed applications, but also in the medium and low power range. While most of the problems related to the feedback control of AC motors have been successfully solved, another crucial point emerged with the diffusion of induction motors: the condition monitoring and the detection of their most common faults. In this work, a novel approach to fault diagnosis of AC motors is introduced. Specifically, the architecture of a nonlinear tracking controller made of an observer and a feedback-linearizing module is exploited in order to generate residual signals to be used for fault diagnosis purposes. In the paper, both simulation and experimental results on a real AC motor are provided showing the effectiveness of the proposed approach.

The estimation of the disturbance torque in a sensorless DC motor drive is carried out by extending the classical observer theory. Three estimation schemes are formulated according to the representation of the disturbance torque and the processing of the observer states. In addition to the disturbance torque, all the schemes deliver an estimation of the motor speed. Steady-state accuracy and dynamics of the schemes are first determined in nominal conditions, identifying the scheme with the best performance. The effects of variations in the motor parameters are then analyzed, with the finding that a proper modeling of the motor makes the steady-state estimation of the disturbance torque insensitive to any variation. As a test, the schemes are applied to a sensorless DC motor drive for both compensating for the disturbance torque and closing the speed loop. The responses obtained with the best-performance scheme are reported. >

The paper deals with an induction motor (IM) speed drive having high performance over a large speed range in the constant torque region. The drive is built up around an outer loop of speed equipped with an incremental encoder and two inner loops of torque and flux implemented in a direct torque control (DTC) scheme. The scheme takes advantage of the available speed to estimate the motor torque and the stator flux magnitude by means of the IM current model. This allows the full exploitation of the drive capabilities even in the low speed range. Furthermore, with a suitable representation of the IM current model, the drive can be operated down up to zero speed. The paper closes by analytically investigating the detuned behaviour of the scheme due to a rotor time constant mismatch. Experimental results substantiate the low-speed capabilities of the scheme and the findings on its detuned behaviour.