Improving Fault Tolerance of Multiphase LCI-Fed Synchronous Motor Drives

Load-commutated inverters (LCIs) are reliable and efficient drives to supply synchronous motors in high power industrial applications. However, inadequate attention is dedicated to this type of drive especially for higher phase numbers and in the case of faults. It is a proven fact that the fault tolerance of the voltage-source inverter (VSI)-fed multiphase machines is enhanced as the number of phases increases. However, the same principle is not necessarily applicable to the LCI-fed multiphase synchronous machine drives. As it will be shown in this paper, a thyristor failure may cause the drive instability and the situation can be more critical for higher phase numbers. In this paper, open-circuit faults and their consequences are investigated and compared for symmetrical and asymmetrical multiphase LCI-fed drives. Also, a new control strategy is proposed to restore the drive stability in the case of open-circuit faults in LCI-fed drives. Simulation results for a five-phase drive show that the control system can efficiently keep the machine synchronism in the event of phase open-circuit faults.