Fault-Tolerant Field-Oriented Control-Based Current-Regulation Strategy of a Six-Terminal Nine-Phase Induction Motor

This paper presents a vector-control-based strategy to regulate the current in a dual three-phase voltage-source inverter (VSI)-fed Six-terminal nine-phase (6T9P) induction motor. The 6T9P winding layout offers the benefits of a lower inverter leg count than the conventional nine-phase topology, thereby reducing control complexity and enhancing fault tolerance. However, the major challenge with this winding topology is the current mismatch between the two three-phase winding sets, abc1 and abc2, which is exacerbated by load dynamics and faults, leading to increased copper losses and torque and speed pulsations. This paper proposes a Field-Oriented Control (FOC)-based current-regulation strategy using Two-Degree-of-Freedom (2DOF) PI controllers and implemented in an arbitrary reference frame. MATLAB2024b /Simulink simulation results demonstrate that the proposed method reduces the Current Unbalance Factor (CUF) from 18.06% to 0.46% under healthy conditions and from 25.1% to 1.04% under a one-phase open fault. In comparison, a reported voltage-to-frequency (V/f) control scheme (existing controller) achieved 0.25% and 80.43% under healthy and faulty conditions, respectively. Additionally, the proposed control scheme improves speed-tracking capability, enhances torque dynamics, and stabilizes rotor flux.