PUBLICATIONS

This dissertation presents control strategies to mitigate inherent control instability in a single inverter dual motor (SIDM) drive system, which operates two permanent magnet synchronous motors (PMSMs) in parallel using a single inverter. PMSM based SIDM systems offer advantages such as simplified hardware configuration, cost reduction, and compact system design. However, due to the limited control degrees of freedom inherent in the single inverter structure and the characteristics of PMSMs, oscillations occur in the rotor position and speed difference between the two motors, which result in speed and torque ripples, resonance, and step-out issues, ultimately degrading the overall stability of the system. These lead to speed and torque oscillations, resonance, and eventual loss of synchronism, thereby degrading system stability. To address these challenges, this dissertation first presents a gain design method for the active damping controller, which optimizes the proportional gain based on the operating conditions. The proposed method formulates a gain model using mechanical stability analysis and least squares method, enabling reliable gain design without the need for extensive experimental tuning, while accounting for variations in speed and load torque. Additionally, a speed synchronization controller is proposed to eliminate the singularity problem that occurs under equal-load conditions in PMSM based SIDM systems. A modified transfer function based on a cosecant structure is employed, incorporating upper/lower bounds and rate limiters to ensure robust damping current generation under all operating conditions. The theoretical validity of the proposed methods is demonstrated through pole analysis based on mechanical modeling, root locus analysis using state-space equations, and resonance frequency-based modeling. Furthermore, their effectiveness is validated through simulation and experimental results under various operating scenarios. The proposed methods provide practical solutions for enhancing synchronization and stability in PMSM based SIDM drive systems.