Advanced Sliding Mode Speed Control Technique for 18-Pulse Rectifier-Fed Three-Level NPC Inverter-Based Induction Motor Drives

Abstract

Conventional proportional-integral (PI) based field-oriented control (FOC) suffers from slower dynamic response, higher torque ripple, and reduced robustness against load disturbances. This paper proposes a modified sliding mode control (SMC) technique for the outer speed loop of an 18-pulse rectifier-fed three-level neutral-point-clamped (3L-NPC) inverter-based induction motor drive (IMD). The 18-pulse rectifier and 3L-NPC inverter are used as an experimental platform, while the proposed contribution focuses exclusively on the speed controller. A Lyapunov-based stability analysis establishes finite-time reaching of a hysteresis boundary layer and bounded quasi-sliding-mode behavior thereafter, and, under a reduced outer-loop approximation and a discrete-time quasi-static filter condition, uniform ultimate boundedness of the outer speed-loop error. Simulation and experimental investigations demonstrate faster speed tracking, improved disturbance rejection, lower torque ripple, and enhanced current quality compared with conventional PI and classical SMC controllers. A reduced-scale experimental setup with a 5kW induction motor (IM) is used to validate the simulation results. Experimental results show that the proposed controller reduces stator current THD to 4.19%, compared with 12.71% for the PI controller and 7.12% for the conventional SMC, while also providing improved neutral-point voltage balance and smoother steady-state waveforms. A comprehensive benchmark comparison with recent advanced SMC methods further confirms that the proposed controller achieves the most balanced overall performance in terms of transient response, robustness, tracking accuracy, and harmonic suppression.