• Energy Research

The energy transition and the decarbonization of transport dictate a switch towards electrification in the naval sector. Ferries, among the different types of ships, are those most suited for a full electrification, consisting in the replacement of engines with electric motor drives and fuel tanks with electrochemical energy storage systems. However, some cost issues and energy storage technological limitations still hamper full electrification, making partial electrification more practical, which can still be effective in reducing pollutant emissions in ports and surrounding areas. The aim of this work is to investigate some issues related to onboard energy storage systems needed for electric ferries. The Ro-Ro Elio ferry, operating in the Strait of Messina is considered as a case study. Some different solutions are investigated, in terms of economic/enviromental efficiency, which is the cost of preventing the emission of a kg of CO2.

This work aims to propose a new powertrain for the ferry 'ELIO' operating in the Strait of Messina. Based on the operating data kindly provided by Caronte&Tourist, the authors suggest an alternative propulsion system with methanol fueled HT-PEM fuel cells and batteries, supported by multilevel converters feeding the electric propulsion motors. The power plant is sized through an optimization process considering fuel cell power levels, battery pack capacity and battery current. The detailed modeling of the multilevel converters allows for accurate evaluation of losses on both converters and electric propulsion motors. Eventually an evaluation of the overall efficiency of the system and the reduction of emissions is presented.

The electrification of ferries requires efficient shore infrastructures that include energy supply grids, communication networks, charging systems, energy storage systems, interfacing and monitoring devices. In this context, a lot of research and development efforts have been made in the last decade that are reviewed in this paper. Energy storage technologies, battery charging requirements and their safety parameters are first analyzed. A comprehensive review on shore side infrastructure design and power system architecture are then provided. Different shore to ship interfaces are finally presented along with, some alternative solutions to battery charging stations.

A multi-level open-end winding converter topology for multiple-motor drives is presented featuring a main multi-level inverter processing the power delivered to the motors and an active filter based on an auxiliary two-level inverter. The main inverter operates at the fundamental frequency in order to achieve low switching power losses, while the active filter is Pulse Width Modulation (PWM) operated to suitably shape the motor currents. The proposed configuration features less phase current distortion than conventional multi-level inverters operating at the fundamental frequency, while achieving a higher efficiency compared to PWM multi-level inverters. Experimental results confirm the effectiveness of such a configuration on both multiple motors-single converter and multiple motor-multiple converter drives.

The paper presents a self-sensing control technique for a special type of multilevel motor drive featuring an Open-end Winding Permanent-Magnet Synchronous Motor fed on one side by a main multilevel inverter (MLI) and on the other side by an auxiliary two-level inverter (TLI). In order to minimize the power losses, the MLI manages the machine active power operating at a low-switching frequency. The TLI instead acts as an active power filter and operates at a higher switching frequency and a lower DC-Bus voltage than the MLI. The current control task is shared between the two inverters, as a predictive action is exerted by the MLI, while a feedback action is accomplished by the TLI. Common sensorless rotor position estimation techniques cannot be straightforwardly applied on such a system, due to the particular drive structure. Therefore, a specific technique has been carried out, able to ensure satisfactory efficiency and control performance in all the operating speed ranges by optimally exploiting the different features of the two inverters. Simulation and experimental results confirm the effectiveness of the proposed approach.

The development and the validation of an averaged-value mathematical model of an asymmetrical hybrid multi-level rectifier is presented in this work. Such a rectifier is composed of a three-level T-type unidirectional rectifier and of a two-level inverter connected to an open-end winding electrical machine. The T-type rectifier, which supplies the load, operates at quite a low switching frequency in order to minimize inverter power losses. The two-level inverter is instead driven by a standard sinusoidal pulse width modulation (SPWM) technique to suitably shape the input current. The two-level inverter also plays a key role in actively balancing the voltage across the DC bus capacitors of the T-type rectifier, making unnecessary additional circuits. Such an asymmetrical structure achieves a higher efficiency compared to conventional PWM multilevel rectifiers, even considering extra power losses due to the auxiliary inverter. In spite of its advantageous features, the asymmetrical hybrid multi-level rectifier topology is a quite complex system, which requires suitable mathematical tools for control and optimization purposes. This paper intends to be a step in this direction by deriving an averaged-value mathematical model of the whole system, which is validated through comparison with other modeling approaches and experimental results. The paper is mainly focused on applications in the field of electrical power generation; however, the converter structure can be also exploited in a variety of grid-connected applications by replacing the generator with a transformer featuring an open-end secondary winding arrangement.

An Open-End Winding system is proposed able to manage the electric generator and the battery energy storage system in a wind power plant with integrated energy storage. The proposed system is formed by connecting a T-Type rectifier and a two-level inverter/rectifier equipped with fast GaN devices through the open stator winding of the AC generator. The T-Type rectifier feeds power to the dc bus of the grid inverter, while the energy storage system is managed by the inverter/rectifier, which acts also as an active power filter to sinusoidally shape the generator phase currents, and as a voltage equalizer to balance the voltage of the output capacitors. A three-port power conversion system with almost negligible switching power losses is obtained, because the T-Type rectifier is operated at very low switching frequency, while low inverter switching power losses are achieved thanks to the GaN devices. Purposely developed modulation and control techniques are exploited to cope with the specific features of the proposed Open-End Winding system. Simulation results confirm the consistence of the proposed system in managing with high efficiency a wind power plant with an integrated battery energy storage system.