A Boost-Type Four-Leg Inverter With Integrated Open-Phase Fault-Tolerance for PMSM Drives

This article proposes a boost-type four-leg inverter for three-phase permanent magnet synchronous machine (PMSM) drives where the power supply is innovatively connected between the neutral point of the motor and the fourth leg. Due to the special connection, the zero-sequence circuit of a PMSM drive fed by the proposed four-leg inverter can not only be used to tolerate an open-phase fault (OPF) but also to boost the dc-bus voltage. According to the analytical modeling and equivalent circuit, it is revealed that the four-leg inverter-based PMSM drive is similar to a two-stage drive under healthy operating conditions. When an OPF occurs, the motor can be normally operated with only two active phases. Under postfault conditions, the remaining phase-currents are not sinusoidal any more. Besides, the trajectory of the postfault current vector is not a standard circle. The traditional field-oriented control strategy can still be adopted in the drive. However, the references of the $d$ -axis current and neutral current have to be modified by injecting specific components. A differential flatness-based controller is proposed to track the time-varying current references. Experiments are carried out on a 1.2-kW PMSM test-bench to verify the effectiveness of the proposed scheme.