Control and analysis of permanent magnet dual-three-phase drives

Multiphase machines constitute a category of electric motors notable for high torque density, reliable operation, and robust performance under fault conditions, making them strong candidates for automotive propulsion. This thesis, conducted during a research period at the PEMC of the University of Nottingham (UK), focuses on stability analysis and control strategies for multiphase electric machines. Initially, an overview of the three-phase machines is presented, including the derivation of all fundamental equations and the associated reference frame transformations. This is followed by an analysis of the mathematical models and control schemes used for speed, torque, and current regulation. From this, the fundamental equations for dual-three-phase machines are derived, along with a description of their topologies and the methodology used for machine characterization. A comprehensive inductance analysis is conducted for both IPM and SPM multiphase machines, accounting for linear and nonlinear B−H material characteristics. Based on the derived values, classical, modified, and autotuned PI controllers are investigated, along with a comparison of various feedforward compensation techniques. The current control strategy is developed using the modular approach and the VSD. Furthermore, instead of relying on inductance values for flux estimation, a control strategy based on a flux observer is proposed and evaluated. All control loops are implemented on the derived machine models to evaluate their effect on system stability and dynamic performance. For current control, which is modelled as a MIMO system, a state-space representation is developed and analyzed through eigenvalue analysis. To validate the theoretical models and control algorithms, detailed studies are carried out in Matlab and Simulink. The simulation results are analyzed to compare the dynamic response and robustness of the various control strategies under a range of operating conditions.