Modelling, Simulation, and Control of Permanent Magnet Multiphase Motors

This thesis presents a comprehensive modelling and analysis of a Dual Three-phase Interior Permanent Magnet (DT-IPM) motor, developed during a research period at the Power Electronics Machines and Control institute (University of Nottingham). The objective is to develop a complete workflow, from physical characterisation to control implementation, capable of performing numerical simulations of a multiphase synchronous machine and testing the performance of different control algorithms. Initially, an analytical model is developed for both the three-phase and dual three-phase systems, focusing on reference frame transformations, apparent and incremental inductance matrix formulations and the differential equations that describe the motor. A Finite Element Analysis (FEA) model is then realised through the adoption of the software Matlab and FEMM 4.2, with particular attention to computational effort optimization and obtaining the rotor geometries via a reverse engineering approach. Results are post-processed obtaining multidimensional Look-Up Tables (LUTs) that represent the main electromagnetic quantities of the machine in the DQ reference frame, including non-linearities and periodic variations with respect to the rotor position. The reverse engineering and validation of the model have been performed comparing the outcomes with experimental measurements, paying particular attention to the Back Electromotive Forces (BEMFs) and phase resistances. Another validation approach is proposed with the analysis of the short-circuit currents of the machine. The results of the FEA are embedded in Simulink environment and used to develop advanced control strategies of the machine. The optimal control trajectories in the DQ reference frame are obtained by post-processing of the FEA results. The gains of the Proportional Integral current controllers are evaluated based on an analysis of the parameters of the machine, and a Feed-Forward compensation approach exploiting a multivariable polynomial regression of the apparent inductances of the machine is proposed. Subsequently, a comparison between the DT-IPM model and an equivalent Dual Three-phase Surface Permanent Magnet (DT-SPM) one is analysed. The investigation focused on mutual-coupling effects in the centralised control approach with Vector Space Decomposition (VSD) and in the modular three-phase one. Finally, a different control algorithm is proposed to address the issue of mutual-coupling effects by controlling the stator fluxes rather than the currents. The resulting machine model is a flexible platform that enables realistic electromagnetic simulation of the motor and allows testing of different real-time control strategies, offering insights into the advantages of multiphase machines as well as the challenges of their control.