Application of an Improved NLGIFO-Based Flux Observer in DTP-CPMSM Sensorless Drives

The sensorless observer serves as a core component of the vector control system for permanent magnet synchronous motor in shaft-less rim-drive thrusters systems. Its accuracy directly determines the performance of the control system. For flux observer, the rotor flux circular trajectory offset and radius distortion caused by the DC bias and parameter mismatch are the primary reasons for the increased rotor position errors. To address these issues, this paper proposed an improved flux observer based on a second-order generalized integrator and a limit cycle oscillator. This method shifts from signal processing to physical-state reconstruction by anchoring a limit cycle oscillator to the nearly constant magnitude of the permanent magnet flux. This physics-based constraint effectively suppresses estimation errors induced by DC bias and enhances robustness against motor parameter mismatch. Moreover, the design eliminates heuristic tuning: its adaptive gain is regulated by the magnitudes of the estimated and actual flux, ensuring stable and fast convergence under complex conditions without introducing additional parameters. Finally, experimental verification was conducted on a 10 kW DTP-CPMSM test platform.