A Robust High-Order Disturbance Observer Design for SDRE-Based Suboptimal Speed Controller of Interior PMSM Drives

This paper proposes a robust high-order disturbance observer (HODO) for the state-dependent Riccati equation (SDRE)-based suboptimal speed controller of an interior permanent magnet synchronous motor (IPMSM) drive. The conventional disturbance observers (DOs) cannot accurately estimate the fast time-varying disturbances of an IPMSM during the transient-state because the disturbances are assumed to change slowly, so the inaccurately estimated disturbances lead to conservative robust control. Unlike the conventional DOs, the proposed HODO guarantees the fast convergence of the estimated error for an IPMSM drive by accurately estimating the fast time-varying disturbances and their all high-order derivatives. Also, it is specifically applicable to the SDRE based suboptimal speed controller which cannot completely eliminate the steady-state error in the presence of mismatched disturbances and uncertainties. Finally, the simulation results via a MATLAB/Simulink package and the experimental results via a prototype IPMSM test-bed having TI TMS320F28335 DSP are presented to verify the faster dynamic response, smaller steady-state error, and more robust response of the SDRE speed controller with the proposed HODO compared with the conventional 1st-order DO, conventional generalized proportional integral observer (GPIO), and conventional SDRE observer.