# 1: LCI requires specially designed motors with low reactance.

• This is a semi-true. Yes, the motors for LCI drives are usually specially designed (e.g. dual star stator, capacitive power factor). Lower stray reactance is an advantage as the commutation notches are smaller. However, LCI also works as a soft starter where the synchronous machine is a normal direct on-line type. LCI prefers lower reactance of motor while VSI prefers higher reactance. This is due to the different nature of both technologies: LCI with current source behavior and VSI with voltage source behavior. However, LCI can drive a motor with higher reactance same as VSI can drive a motor with lower reactance. In both cases the system is sub-optimal, but it is feasible.

# 2: LCI has higher air gap torque harmonics.

• This is generally not true. LCI with 6-pulse inverter has quite high pulsations of air gap torque. It is frequently used in applications such as soft starters or gas turbine starters, i.e. not for continuous operation. LCI drives almost always have 12-pulse output consisting of two 6-pulse bridges. The motor has dual three-phase stator winding with 30 deg relative displacement between windings (Y0Y30). This state of the art arrangement drastically reduces the torque ripple. 6-pulse inverter working with firing angle 165 deg has min. torque 70.7%, max. torque 100%, average torque over the period 92.2% and torque ripple (max-min) 29.3%. The 12-pulse configuration has about 3-times lower ripple, i.e. value comparable with VSI drives.