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 permanentmagnet synchronousmachine (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.