Noncascade Structure Equivalent SMC for PMSM Driving Based on Improved ESO

An equivalent sliding mode control method with a noncascade structure is proposed to improve the response speed and the robustness of the permanent magnet synchronous motors speed control system. First, the design of the equivalent sliding mode control law for the second order system is performed. This leads to a direct output of the q-axis voltage from the controller. As a result, the current loop is eliminated, the system structure is simplified and the bandwidth is increased. Second, the state-space equations are reconstructed based on the sliding mode surface so that the mechanical and electrical disturbances of the system are merged. As a result, all disturbances can be estimated by a single extended state observer, and multiple disturbance observers or complex observer matrixes are no longer required. Afterwards, the gain of the extended state observer is modified to a nonlinear time-varying form. Thus, the peak phenomenon of the observer is reduced. Then, the number of samples per beat of extended state observer is increased to four according to the space vector pulse width modulation (SVPWM) output principle. Which improves the phase angle margin and signal-noise ratio of the observer. Finally, the current amplitude constraint and one-beat delay are properly handled to ensure the reliable operation of the controller. Experimental verification is also carried out to demonstrate the superiority of the proposed method.