Optimizing the Connection Diagram and Turns Number for the Three-Phase to Multiphase Transformer Converter Secondary Winding Coils

Abstract

An approach to determining the optimal connection diagram and the number of turns for secondary winding coils of a three-phase to multiphase transformer-type converter is considered. Each phase of the device’s multiphase winding comprises three coils placed on different core limbs and connected in series with each other. To determine the connection diagram and the number of turns in the multiphase winding coils, it is necessary to solve an optimization problem with taking into account certain constraints that will make it possible to obtain the same number of turns in the series-connected coils of each secondary winding phase, a symmetrical multiphase EMF system, and uniformly distributed symmetrical multiphase load among the three primary winding phases. The formulated optimization problem with constraints is solved using the numerical interior point method. The application of the proposed approach is illustrated by an example of calculating the minimum number of turns in the coils of a three-phase to seven-phase converter, and the converter windings connection diagram is presented. The article gives the calculated apparent power values of the secondary winding coils with a symmetrical resistive-inductive load for a converter with different numbers of coil turns evaluated from solving the optimization problem with various constraints. A prototype three-phase to seven-phase converter has been fabricated on the basis of a three-phase transformer of a standard series. As a result of experimental studies of the prototype, the seven-phase winding instantaneous voltage waveforms, r.m.s. values of currents and voltages, and the primary winding power for no-load and symmetrical load modes have been obtained. The experimental study results have confirmed the calculation results adequacy. By using the proposed approach, it is possible to design a three-phase to multiphase converter with the number of multiphase secondary winding phases more than two. The designed secondary winding coils will have the minimal number of turns, which will make it possible to manufacture a device with smaller mass and dimension indicators and decrease the consumption of expensive electrical materials.