Based on the nonlinear characteristics of permanent magnet synchronous motor (PMSM), a nonlinear speed and direct torque control (DTC) using sliding mode backstepping method for PMSM is presented in this paper. The sliding mode speed controller is implemented with exponential reaching law to improve the robustness of the system, and further a step-by-step recursive design for backstepping torque and flux controllers is presented. The system stability with proposed scheme is mathematically proved using Lyapunov stability criteria. At the same time, the load torque is observed with the extended state observer (ESO), and is fed-forward to the controller for rejecting the load disturbance and to mitigate the chattering affect due to the sliding mode controller. Finally, simulation test results are demonstrated to support the effectiveness and feasibility of the proposed strategy.

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Stator flux estimation for electrical machine using voltage model (VM) with a simple structure and the least parameters has been widely researched in high-performance drive systems. Existing low-pass filter (LPF)-based estimators either respond slowly or cannot adequately suppress DC drifts, thus, a vector transforming and signal filtering method using VM is proposed for flux estimation. An original flux vector is directly produced through a transformation for motor back electromotive force, and then, the desired flux is obtained through an optimised filter which is designed by combing LPF and band-pass filter with an optimal function. The proposed estimator can both eliminate DC drifts and obtain a fast response and high accuracy, and additionally, its structure is simplified by the decomposing process, which significantly reduces the computation and occupied resources. The effects of cutoff frequencies on dynamical responses and flux harmonics are investigated and the limitations are obtained. This estimator is applicable to extensive strategies, for instance, the implementation of a direct torque control-based electrical drive system is carried out. Theoretical analysis, simulation, and experiment are conducted to validate the feasibility and effectiveness of the proposed scheme.