Modification of Park variable transformation for wye-connected winding without neutral wire

Purpose The purpose of this paper is to present a modification of the Park variable transformation for a three-phase wye-connected winding without neutral wire. A new physical interpretation of the winding equivalent circuit is proposed. Design/methodology/approach An equivalent circuit representing reluctance motor stator winding is rearranged to enable easier physical interpretation of obtained voltage equation. The Park transformation and constraints resulting from Kirchhof's laws are then applied to obtain a two-axis mathematical model of the motor. Findings A new physical two-phase interpretation of the voltage equation for a three-phase wye-connected winding without neutral wire is proposed. A novel two-axis transformation is formulated for all variables. Compared to the Park transformation, which is the same for all variables, in the proposed transformation its matrices for currents and voltages/flux linkages are different, yet strongly interconnected. Research limitations/implications The proposed transformation is formulated for a specific type of winding connection scheme. Therefore, it is limited in its application. Practical implications From the practical point of view, the proposed transformation could be very useful as it applies to the most popular stator winding connection scheme. Its main advantages are fewer number of trigonometric parameters in the matrices and measurability of all currents and voltages present in its voltage equations. It could be of special importance for electric machines with non-sinusoidal field distribution (e.g. Brushless DC). Originality/value The paper presents a new type of variable transformation for three-phase electric machines with wye-connected windings without neutral wire. Proposed transformation combines different transformations for currents and voltages/flux linkages.