Comparative performance study of alternate fault-tolerant inverter configurations for direct torque control-based three-phase PM BLAC drives under single-phase open-circuit fault

Abstract

This paper presents a comparative performance study of three typical fault-tolerant control (FTC) topologies [split-capacitor (SC), extra-leg split-capacitor (ELSC), and extra-leg extra-switch (ELES)] for direct torque control (DTC)-based three-phase permanent magnet (PM) brushless AC (BLAC) drives under single-phase open-circuit fault (SOF). The advantages and limitations of these FTC schemes are theoretically compared and empirically validated. To achieve reliable postfault operations, control issues associated with VM-based flux estimators employed for DTC-based BLAC drives under SOF are demonstrated and relevant remedies are proposed. It is shown that although the ELES scheme can maintain the normal based speed, 6 of its 8 switching states cause phase-to-neutral short circuit in one or both two remaining phase windings resulting in high current harmonic values. Besides, during its implementation, the full DC-link voltage value is always applied to the non-short circuit phase windings leading to high possibility of winding insulation damage. Thus, for a compromise of the normal based speed by a factor of √3/2, the ELSC drive should be used to avoid these issues. Furthermore, in the low-speed region up to half of the rated speed, the lowest copper loss, current harmonics, and torque ripples can be obtained by utilizing the SC drive.