Four switch three phase inverter fed PMSM DTC system with nonlinear perpendicular flux observer and sliding mode control

Four-switch three-phase inverter (FSTPI) is usually adopted as the topology for continuous fault-tolerant operation of a direct torque (DTC) system when inverter fault occurs. Due to that the FSTPI can only provide four voltage space vectors with unequal amplitude, the DTC system performance will deteriorate to a certain extent. To enhance the performance of permanent magnet synchronous motor (PMSM) drive fed by FSTPI, a sliding mode controller with the analysis and design of the controller included is proposed for the purpose of direct control the torque and stator flux linkage in this paper. Besides a nonlinear perpendicular flux observer is adopted to estimate the stator flux more accurately as well. The effectiveness of the proposed methods have been verified by simulation study, in which the torque and flux ripples have been significantly minimized and the inherent merits of fast dynamic responses of the conventional direct torque control are preserved.