Decoupled Control of Series-Connected Split-Phase Synchronous Motors With Open-Circuit Fault With Eight-Legged Inverter

Multiphase drives are preferred in applications where low torque ripple, fault tolerance, and higher power density are requirements. Split-phase machine is a widely used multiphase machine type with two sets of three-phase windings, each set shifted by 30°. This configuration eliminates the sixth-harmonic torque pulsations. Control of series-connected split-phase machines is studied extensively, and the configuration is advantageous compared to conventional two-inverter drive systems in terms of number of semiconductor switches used. However, when open-circuit (OC) faults occur in series-connected systems, both motors would generate very high torque pulsations. In this article, a decoupled control strategy with zero torque pulsations for series-connected synchronous split-phase motors under OC fault condition is presented. Postfault magnetomotive force (MMF) equations to obtain a constant rotating magnetic field are developed and presented for the series-connected system. This is achieved by applying a voltage to the neutral terminal using an additional inverter leg. This enables the operation of series-connected synchronous motors with zero torque ripple while simultaneously ensuring decoupled control under OC fault conditions. Exhaustive experimental results for steady-state, transient, and fault operations are presented for validating the proposed concept.