Reduced Parameter Sensitivity Stator Flux Linkage Observer in Deadbeat-Direct Torque and Flux Control for IPMSMs

Direct torque control (DTC) has become a widely acceptable alternative to field oriented control (FOC). Deadbeat-direct torque and flux control (DB-DTFC) is a significant improvement over the classical DTC methods and provides the opportunities for fast simultaneous control of torque and dynamic loss minimization. DB-DTFC uses estimated torque and stator flux magnitude from a stator flux observer as feedback. The constant parameter state observer utilizes the system model to estimate immeasurable physical states or dynamics of the real system. However, the constant parameter stator flux observer is parameter sensitive at low frequencies. This paper presents a flux observer that utilizes disturbance input decoupling (DID) so that even under varying or inaccurately identified machine parameters, stator flux linkage and torque can be accurately estimated. The structure of the DID flux observer is theoretically derived and discussed. The flux estimation error due to the parameter variations is decoupled through the disturbance information from a stator current observer. Comparative evaluation of the DID flux observer versus the constant parameter flux observer has been performed via both simulation and experiments.