Reduction of harmonic distortion in electromagnetic torque of a single-phase reluctance motor using a multilevel neutral-point-clamped DC-AC converter

The harmonic performance, control robustness, and thermal characteristics of single-phase multilevel neutral-point-clamped (NPC) converters driving a single-phase reluctance motor (SPRM) are comprehensively analyzed in this study. Three converter topologies—a two-level single-phase NPC (2L-1P-NPC) converter, a three-level single-phase NPC (3L-1P-NPC) converter, and a four-level single-phase NPC (4L-1P-NPC) converter—are investigated under four modulation schemes: bipolar voltage pulsewidth modulation (BVPWM), unipolar voltage pulsewidth modulation (UVPWM), level-shifted pulsewidth modulation (LSPWM), and virtual-vector pulsewidth modulation (VVPWM), all operating at a fixed switching frequency of 10 kHz. High-fidelity simulations conducted in MATLAB-Simulink accurately replicate the coupled electromagnetic, mechanical, and thermal dynamics of the SPRM system, utilizing realistic motor and load parameters to ensure application-level relevance.

The results demonstrate that increasing the converter level substantially reduces total harmonic distortion (THD), with the 4L-1P-NPC topology under LSPWM achieving the lowest THD of 23.66%, thereby significantly improving voltage waveform quality and minimizing electromagnetic torque ripple. A proportional–integral (PI)-based feedback controller is implemented for velocity and position regulation, yielding precise trajectory tracking, a fast transient response, and negligible steady-state error. Additionally, thermal analysis quantifies power losses—conduction, switching, core, and copper—highlighting the trade-off between improved harmonic/dynamic performance and increased thermal stress. Notably, the junction temperature escalates from 121.8℃ in the 2L-1P-NPC converter to 188℃ in the 4L-1P-NPC converter, underscoring the necessity for advanced heat dissipation strategies in high-power applications.

By integrating harmonic distortion mitigation, closed-loop control design, and thermal evaluation, this work presents a unified framework for the optimal design and analysis of high-performance, thermally aware multilevel SPRM drives.