Improved control of load commutated inverter fed salient pole wound field synchronous motor using field oriented technique

Abstract

Load commutated inverter (LCI) fed wound field synchronous motor (WFSM) is used for high speed, medium voltage, high power industrial applications. The control popularly known as “self control” is well reported for cylindrical rotor WFSM. Such a control when applied for salient pole WFSM becomes complex due to saliency and requires rigorous off-line calculations for generation of look up tables etc. In addition, the self control technique does not include cancelling out the coupling between torque and flux control which exists in salient pole WFSM. In this regard, this paper proposes to adopt field oriented control, generally used with voltage source inverter fed drives, for the control of salient pole WFSM fed from LCI. It offers many advantages over self control technique besides providing accurate control such as decoupled flux and torque control, simple real-time calculation of field current over-excitation considering instantaneous load torque as well as speed of the motor, sensor-less techniques, simplification in SCR gate pulse generation etc. In this paper the starting of the LCI, which is generally done using “dc-link current pulsing” technique, is not considered. The performance of the drive is demonstrated with elaborate experimental observations on a 15.8 hp salient pole WFSM.