Power Factor Improvements for Load Commutated Inverters

Abstract

This paper is concerned with the control and operation of load commutated inverter-fed synchronous machines, and in particular with the selection of the firing angles on the machine side of the load commutated inverter. An extension to the previously published Model Predictive Torque Control was developed, which improves the operation of load commutated inverters at steady state. The main benefits of applying this control method are an improved power factor and reduced reactive power consumption, with a simultaneous increase of drive efficiency and reduction of the harmonic content of the line side currents and of the air gap torque. Further, the stator and field currents are reduced, reducing the temperatures in the machine and the transformer, which ultimately increases the lifetime of the equipment. Alternatively, the power factor improvements can be utilized for increasing the output power of the synchronous machines. The findings are validated on a reference industrial site comprising three load commutated inverter-fed synchronous machines with a nominal shaft power of 7.5 MW each.