An improved sensorless DTC-SVM for three-level inverter-fed permanent magnet synchronous motor drive

A speed-sensorless control strategy is investigated in a wide speed range based on extended Kalman filter (EKF) and direct torque control with space vector modulation (DTC-SVM) for three-level cascaded H-bridge inverter-fed permanent magnet synchronous motor drives. The implementation of conventional SVM technique to the multilevel inverters is considerably complicated and leads to high computational burden. A three-level SVM technique simplified on the basis of two-level voltage vector diagram is proposed to reduce this computational complexity, and in addition, to satisfy some requirements for the safe operation of the inverter such as smooth commutation and minimum number of switching. The estimations of rotor position and speed are achieved using an EKF without high-frequency signal injection, especially at very low and zero speeds. The load torque is also estimated simultaneously to account for the mechanical frictions at steady state to improve the estimation performance. Furthermore, the flux trajectory control based on maximum torque per ampere algorithm is implemented to ensure maximal efficiency for constant torque region. The feasibility and effectiveness of the proposed drive system is tested under different operating conditions and verified by the simulation results.