Optimal reactive power ow in BDFMs for converter cost reduction and efficiency improvement

Abstract

A brushless doubly fed machine is equipped with two decoupled windings on its stator, known as the power winding and the control winding. The power winding reactive power can be controlled by voltage amplitude fed by the machine-side converter to the control winding, affecting both the converter size and machine efficiency. This paper investigates different proposed scenarios for optimal reactive power ow targeted to minimize the converter cost and maximize the machine efficiency. Previously, the grid-side converter has not been used for reactive power compensation. However, in the present paper it is shown how the grid-side converter can be effectively used to reduce the converter cost by controlling the ow of reactive power. The optimal power winding reactive powers for minimizing the converter cost and for maximizing the output power are not the same. Then the priority of minimizing converter cost over maximizing machine output power has been justi ed.