Cascaded Direct Torque Control of Unbalanced PMSM With Low Torque and Flux Ripples

During operation or manufacturing, the electrical machines are often exposed to parasitic impedance in the phases, causing unbalanced three-phase currents and increased torque and flux ripples. To mitigate the undesired torque and flux ripples, this paper presents a modified cascaded direct torque control strategy for three-phase PMSMs, having asymmetric phase impedances. The proposed method aims to generate the positive and negative reference voltage vectors by extracting the sequential components of the stator flux and current in the stationary alpha beta frame. Then, these two vectors are combined to produce the modified reference voltage vector for space vector modulation. Moreover, for further torque ripple suppression, a standard proportional-integral regulator has been enhanced by a resonant controller tuning at twice of the fundamental frequency. Various experimental results verify the feasibility of the proposed strategy under dynamic and steady-state conditions.