Torque Ripple Mitigation in ۱ MW Seven Phase Induction Motors Under Open Phase Faults Using SS-ENMPC and EKF WRLS Adaptive Harmonic Optimization

Multiphase induction motors, especially the seven phase type, are considered an ideal choice for high power applications such as all electric ship propulsion and offshore wind turbines due to their high fault tolerance capability and low torque ripple. However, the occurrence of an open phase fault in the stator creates severe asymmetry, introduces disturbing harmonics, and significantly increases torque ripple, seriously jeopardising the stable operation and efficiency of the system. In this paper, a novel hierarchical control structure based on a Self Stabilising Extended Nonlinear Model Predictive Control (SS ENMPC) controller together with adaptive harmonic optimisation using a hybrid algorithm of a two level Extended Kalman Filter and Weighted Recursive Least Squares (EKF WRLS) is proposed. The main novelty of this research lies in the simultaneous integration of three concepts – “self stabilising”, “nonlinear model predictive control” and “online adaptive optimisation of third and fifth harmonics” – within a two layer architecture. The upper layer computes online the optimal amplitude and phase of the harmonic currents with the aim of minimising a combined objective function that includes the square of the torque ripple and the copper losses. The lower layer, using the extended state space model of the motor under one phase and two phase open circuit conditions, tracks the optimal voltage components simultaneously in the fundamental, third harmonic and fifth harmonic subspaces. Extensive simulations are carried out in the MATLAB/Simulink environment on a ۱ MW seven phase induction motor under various fault scenarios, sudden load changes and speed variations. Quantitative results show that, compared to conventional methods and even advanced machine learning based methods, the proposed method reduces torque ripple by up to ۶۸%, total harmonic distortion (THD) of the current by up to ۵۴%, and copper losses by up to ۳۱%. Furthermore, spectral (FFT) analysis of torque and current confirms the effective elimination of the ۶th, ۱۲th and ۱۸th order harmonics. Sensitivity analysis and Monte Carlo simulations also demonstrate the stability and robustness of the proposed method against parametric uncertainties and measurement noises. The main achievement of this research is the presentation of a fully implementable, robust, low computational burden control solution for critical, high power applications that ensures system reliability and efficiency under fault conditions without requiring experimental infrastructure, relying solely on advanced simulations