Robust Backstepping Control of Parallel-Connected Inverters Supplying an Induction Motor Under Inverter Fault Conditions

This paper proposes a fault-robust backstepping-based control strategy for induction motor (IM) drives fed by parallel-connected voltage-source inverters (VSIs). The developed control scheme is engineered to achieve precise speed tracking, optimal current sharing among parallel inverter legs, and effective suppression of zero-sequence circulating currents (ZSCCs) under both normal operation and inverter fault scenarios. Initially, a comprehensive mathematical model of the parallel inverter-fed IM drive is formulated in the synchronous reference frame, rigorously incorporating the inter-inverter coupling dynamics. Utilizing Lyapunov stability theory, a nonlinear backstepping controller is subsequently synthesized to guarantee closed-loop stability and the asymptotic convergence of tracking errors. To evaluate the robustness and fault-tolerance of the proposed method, open-circuit faults in the inverter power switches are investigated. The dynamic impacts of these faults on motor speed, electromagnetic torque, stator currents, current distribution, and ZSCCs are thoroughly analyzed through both simulation and experimental validations. The experimental findings indicate that the proposed controller successfully sustains stable speed regulation, enhances current sharing, and significantly mitigates circulating currents and torque ripples during fault conditions. Furthermore, comparative evaluations against conventional proportional–integral controllers highlight the superior transient response and enhanced fault resilience of the suggested approach. Ultimately, these results substantiate the efficacy of the proposed backstepping-based control framework in ensuring highly reliable operation of parallel inverter-fed IM drives across diverse operating states.