Stability Analysis of Constant Margin-Angle Controlled Commutatorless Motor

The constant margin-angle control is a triggering control scheme applied to a load commutated inverter to eliminate the commutation failure and to increase the system power factor. The instability of the commutatorless motor operated with this control scheme is analayzed. Basically, two types of instability are found: one due to the negative equivalent resistance and the other due to the angle feedback. The methods to prevent such instability are also proposed and discussed. The analysis results are confirmed by digital simulation and experimental data.