Third-Order Sliding Mode Fault-Tolerant Control of Parallel Multilevel Inverter-Fed Dual-Star Induction Machine Drives for Sustainable High-Power Applications

The growing demand for sustainable high-power electric drive systems requires advanced control strategies capable of ensuring high efficiency, operational reliability, and continuous service under fault conditions. Parallel multilevel inverter-fed dual-star induction machine (DSIM) drives have emerged as a promising solution for medium- and high-power industrial applications due to their modular structure, improved output waveform quality, and inherent fault-tolerant capability. This paper proposes a third-order sliding mode control (TOSMC) strategy to improve the fault-tolerant performance and robustness of DSIM drives operating under open-circuit faults in inverter switching devices. The proposed nonlinear controller is systematically compared with conventional sliding mode control (SMC) and super-twisting sliding mode control (STSMC) under both healthy and faulty operating conditions. Particular attention is given to the influence of freewheeling diode conduction during insulated gate bipolar transistor (IGBT) open-circuit faults, which significantly affects current quality, electromagnetic torque, and overall drive stability. A comprehensive performance evaluation is conducted in MATLAB 2021/Simulink by assessing dynamic speed tracking, electromagnetic torque response, stator current quality, and total harmonic distortion (THD). The results demonstrate that the proposed TOSMC achieves the highest robustness and fault-tolerant capability among the investigated control strategies. Under healthy conditions, the line current THD is reduced from 3.62% and 3.74% using SMC to 1.15% and 1.45% for the two stator stars, corresponding to reductions of approximately 68.2% and 61.2%, respectively. Under open-circuit fault conditions, THD is further reduced from 15.72% to 5.19% and from 12.27% to 4.44%, representing improvements of approximately 67.0% and 63.8%, respectively. Furthermore, the proposed controller effectively suppresses torque oscillations and maintains stable speed regulation despite severe inverter faults. By significantly improving power quality, reducing electrical and thermal stress on power electronic devices, and enhancing system reliability with lower maintenance requirements, the proposed TOSMC contributes to the sustainable operation of high-power electric drive systems. The presented results confirm that third-order sliding mode control constitutes an effective next-generation nonlinear fault-tolerant control solution for parallel multilevel inverter-fed electrical machine drives.