Innovative approaches for power conversion from renewables

This thesis summarizes the main results achieved during my Ph.D. research focused on power conversion from renewable energy sources. Two case studies are presented, exploring innovative approaches to renewable energy technologies. The first focuses on a solution for energy storage, i.e. Flywheel Energy Storage Systems (FESS). The innovative idea is to employ FESS as an alternative to chemical batteries for energy storage when coupled with a residential photovoltaic panel. An ironless dual-rotor electric machine prototype, is presented. The prototype has been designed for FESS application to increase its self-discharge duration time. An analysis of the machine is provided with simulations and experimental tests. Performances are assessed both from the mechanical and electromagnetic domains. Moreover, different motordrive solution are explored. As for the complete FESS, a tool simulating the power flow between all the nodes for energy savings estimates is presented. It allows to find the best match between the size of the system components and the power profiles of PV generation and electric load consumption. The second case study focuses on power conversion for wind energy. An innovative configuration for a Permanent Magnet Synchronous Motor is proposed. This solution is the Opened End PMSM (OW-PMSM) fed by a dual inverter. This motordrive presents advantages making them an ideal technology for wind turbines, e.g. higher energy density and higher fault tolerance. However, it is affected by a Zero Sequence Current (ZSC) circulation that significantly decreases its performances. ZSC must be minimized through proper modulation of the phase voltages. Moreover, switching losses are double the one of a conventional single inverter. A modulation technique based on Discontinuous Pulse Width Modulation is proposed to cancel out the ZSC while achieving a consistent reduction of the switching losses of the double inverter system. The technique is explained in detail and validated with experimental tests.