Permanent Magnet AC Machines for LCI-fed Medium Voltage Applications

This paper presents the possible ways of using permanent magnet AC (PMAC) motors in high power (HP), medium voltage (MV) applications. In these applications, the thyristor-based load-commutated inverter (LCI) is preferred due to its high reliability, efficiency, low cost, and ruggedness over other converters. To ensure the load commutation, the motor should draw leading current from the inverter. In case of wound rotor synchronous machines, this is realised by over-exciting the field. In the literature, several drive configurations using LCI are proposed to feed induction motors. PMAC motors are efficient and energy-dense compared to induction and wound rotor synchronous motors. Therefore, in this paper, the magnet shape and configuration are investigated so that PMAC motor can be used with LCI. Detailed FEM-based simulation study is carried out to arrive at a suitable magnet shape and configuration so that its operating power factor becomes leading and, therefore, it can be now fed directly by LCI. Six different rotor geometries have been studied, and the most optimum configuration is suggested.