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This thesis describes the last three years work and the results achieved after several stages of design and experimental validation. The main result is the development of a novel sharing current controller for multi-three-phase electrical machines. The proposed regulator, called "speed-drooped" or simply "droop" controller, allows the current transient triggered by a step change within the rotating reference frame to be controlled. Since multi-three-phase systems appear to be very good candidates for future Integrated Modular Motor Drives and next transportation system challenges, the work has been set up with modularity and redundancy for next future motor drives.\ud During the preliminary stages, the mathematical models of the droop controller have been derived and validated on a multi-drive rig with two three-phase induction motors on the same shaft at the University of Nottingham. After, while developing a new general purpose control platform for power electronics able to control up to three three-phase systems, the Vector Space Decomposition for de-coupling the mutual interactions within multi-three-phase electric motors has been studied. Thanks to it, the inductance matrix of a triple-star two poles synchronous generator at the University of Trieste, Italy, has been diagonalised. Finally, the proposed current controller has been experimentally validated on a nine-phase synchronous generator and compared with the state of the art current sharing techniques. Furthermore, a post-fault compensation strategy has been formulated and validated by means of simulation work.\ud If compared to the state-of-the-art current sharing techniques, the "droop" regulator capability of controlling current sharing transients while keeping constant speed of the shaft has been proven and successfully demonstrated by means of Matlab/Simulink simulations and experiments on both rigs.

The transportation electrification process is rapidly demanding for drivers with enhanced performance. Modern systems are moving from fossil fuel technologies toward hybrid and fully electric solutions. Consequently, in automotive and motorcycle sectors the complete electrification process requires significant power and energy capabilities, and high efficiency. Also, to minimize the mechanical power loss and save the battery energy, the weight and volume of the vehicle have to be minimized. These features are significantly stressed in race applications, where the power density of the drive and its efficiency has to push the limits of state of the art. In this work, a multiphase machine with dual rotor architecture is employed, aiming at maximizing the performance of a full electric motorcycle (E-Bike). In particular, it is already known that in multi-phase machines it is possible to inject high frequency current component to increase the power density of the drive. Therefore, the analytical model for the injection of a third harmonic in the currents waveforms is presented for a case study of E-Bike featuring a dual rotor with Halback permanent magnet array. The third current harmonic is injected keeping the same peak current, when compared with the control technique without injection. The three-phase and multiphase winding layout of the machine are compared with and without current injection control by means of analytical equations. Finally, finite element results are shown in order to validate the model, the advantage of the multiphase winding and the current injection technique.

This paper presents a droop-based dis- tributed control strategy for multi-three-phase machines that provides augmented controllability during power shar- ing transients. The proposed strategy is able to mitigate the mutual interactions among different sets of windings without controlling any sub-space variable, also offering a modular and redundant design. On the contrary, in a centralised configuration sub-spaces would be controlled using the Vector Space Decomposition, but fault tolerance and reliability levels required by the stricter regulations and policies expected in future transportation systems would not be satisfied. The proposed method is analytically com- pared against the state-of-the-art power sharing technique and equivalent models and control design procedures have been derived and considered in the comparison. Uncon- trolled power sharing transients and their effects on mu- tual couplings among isolated sets of windings have been compared against the proposed regulated ones. Experi- mental results on a 22kW nine-phase multi-three-phase synchronous machine rig validate the design procedures showing good agreement with the expected performances.