Per-Phase Stator Resistance Estimation Using Full-Order Model for Dual Three-Phase PMSM Drives

This article addresses control performance degradation and localized overheating risks in dual three-phase permanent magnet synchronous motor (DTP-PMSM) systems caused by time-varying phase resistances. A milliohm-level per-phase resistance estimation method is proposed by combining a full-order model with a recursive least squares (RLS) observer. A full-order model with a nondiagonal resistance matrix is established in the synchronous coordinate system, revealing the coupling mechanism of unbalanced stator winding resistances across subspaces. The rank deficiency in the multivariable observer is resolved by incorporating the full-order model and the dynamics variation characteristics of the rotor position. A forgetting-factor RLS observer is subsequently constructed to achieve six-dimensional per-phase resistance estimation. Direct current injection in the harmonic subspace is implemented to amplify the resistance voltage drops, enabling full operational range estimation. Simulation and experimental results demonstrate rapid convergence and stable tracking under load transients, temperature variations, and phase resistance imbalances. The method independently estimates milliohm-level resistance increments, providing a verifiable technical solution for condition monitoring and system safety enhancement in DTP-PMSM systems.