Performance Improvement of Direct Torque Controlled IPM Drives by Employing a Linear Combination of Current and Voltage Based Flux Observers

摘要

Flux observers in direct torque controlled (DTC) motor drives are of paramount importance asudthe drives rely on estimated variables for feedback control. It is well known that current based (CB)udestimations are advantageous at low speeds, whereas voltage based (VB) estimations are more accurate atudhigh speeds. Hence, a large number of state-of-the-art DTC drives utilize closed loop flux observers inudwhich the CB and VB estimations become dominant at low and high speeds, respectively. However, it hasudbeen discovered that the performance and current waveforms with the closed loop observers significantlyuddeteriorate at low speeds since the residual error of the VB estimation causes current distortions. Inudaddition, these observers have nonlinear flux transition trajectory resulting in reduced accuracy duringudtransitions. To improve the low speed performance and achieve the linear transition, an alternativeudcombination of the two estimations is proposed. Experimental results on a 10kW interior mountedudpermanent magnet (IPM) machine drive designed for electric vehicle traction applications validateudsignificant improvements on the drive performance