Open-Circuit Fault Diagnosis Method for the Dual Three-Phase Permanent Magnet Synchronous Motor Drive in the Fault-Tolerant Mode

Dual three-phase permanent magnet synchronous motors (DT-PMSMs) can operate in the fault-tolerant mode with the minimum copper loss (MCL) or the maximum torque (MT) under the single-phase fault. However, the amplitude increases and uneven distribution of winding currents in the fault-tolerant mode will induce the drive open-circuit fault (OCF), including the OCF of a certain power switch and the open-phase fault (OPF) caused by the OCFs of two power switches in the same leg. This article proposes the diagnosis method for these two most common OCF types in the drive. Firstly, the principle of fault-tolerant operation and current distribution based on the vector space decomposition are analyzed. Secondly, the analytical expressions of the winding current and the harmonic plane current (x-y plane current) in two fault-tolerant modes with OPF and power switch OCF are derived, and it is found that the x-y plane current has more obvious fault characteristics than the winding current. Furthermore, considering the interference caused by noise and changes in operating conditions, the fault threshold is defined based on the variation interval of the normalized x-y plane current, and the polarity of x-y plane current is combined to identify and locate the fault. Finally, the experiment shows that the proposed method can effectively diagnose the drive OCF within one fundamental current cycle. In the face of sudden changes in speed and torque, including the load is increased from 0.35 times rated load to 0.62 times rated load while keeping the speed unchanged and the speed is increased from 0.3 times rated speed to 0.6 times rated speed while keeping the load unchanged, the fault factor remains stable and will not trigger misdiagnosis.