Extended State Observer Based Stator Flux Linkage Estimation of Nonlinear Synchronous Machines

Synchronous machines (SMs) represent nonlinear dynamical systems with stator flux linkages being crucial for controller design. Among the developed methods for flux linkage estimation, the disturbance observer-based flux linkage estimator (DOB-FLE) is recognized as the state-of-the-art. However, DOB- FLE faces challenges in ensuring exponential convergence during transient conditions. To address this, this paper introduces an extended state observer-based flux linkage estimator (ESO- FLE), which represents an advancement over DOB-FLE. This novel approach utilizes extended states to model the nonlinear disturbance term as time-varying ramp signals, offering a degree of freedom compared to the constant assumption imposed for DOB-FLE and allowing for the estimation of both the extended states and the flux linkages through an ESO. Simulation results from a 35-kW SM drive demonstrate that ESO-FLE achieves exponential performance under transient conditions compared to DOB-FLE.