Enhanced Direct Torque Control for a Three-Level T-Type Inverter

Direct torque control (DTC) is a widely used approach for motor drives due to its distinctive advantages, e.g., fast dynamic response and highly robust against motor parameters uncertainties and external disturbances. To achieve a lower torque ripple, a higher switching frequency is usually required, which, however, can reduce the drive efficiency. Using the emerging silicon carbide (SiC) devices, which can operate efficiently at a much higher switching frequency than their silicon counterparts, thus, it could be feasible to achieve high efficiency and low torque ripple simultaneously. In this work, a novel multilevel DTC for a SiC T-type inverter is proposed to significantly reduce the torque and flux ripples while retaining the fast-dynamic response. The unbalanced dc-link is a common issue of the T-type inverter, which may also lead to a higher torque ripple. To address this issue, the proposed DTC algorithm only uses the real voltage space vectors and virtual space vectors (VSVs) that do not contribute to the neutral point current such that an inherent dc-link capacitor voltage balancing can be achieved without using any active dc-link voltage controls or additional dc-link voltage and/or current sensors. The feasibility and effectiveness of proposed methods are verified by using both simulation and experimental studies.