Modulation in Stator Flux Control of Induction Motor for Reduced Torque Ripple

The paper introduces an improved modulation method for Immediate Flux Control (IFC) of VSI-fed induction motor drive. IFC with single active voltage vector modulation, which is based on direct current control (DCC), reduces the commutation frequency in comparison with SVM [1]-[3]. With this method, an appropriate active voltage vector v(I) is impressed only during a precalculated time interval t(on) (1-6) within the sampling interval Delta(t) to minimize the predicted stator flux error epsilon(lambda) (Fig. 1). In the same manner, the new modulation approach combines complementary durations (7-13) of two optimal active voltage vectors v(I) and v(II) within the sampling interval (Fig. 2). Both active vectors are selected according to the sector of stator voltage reference v(S)* (Fig. 3, Fig. 4, and Table 2). Simulation results for an induction motor (Table 3), being controlled by IFC and predictive torque control (PTC) [4], show improved stator flux accuracy (Fig. 5, Fig. 6), while the commutation frequency is slightly increased; nevertheless it is still lower than in SVM. Torque response (Fig. 7) of the proposed method is as fast as in DTC [5]-[12] with significantly reduced torque ripple (Fig. 8). On the other hand, this modulation method has an important drawback, since the dead-time insertion between non-subsequent active voltage vectors requires major modifications in established control of inverter.