Evaluation of Control Strategies for Permanent Magnet Synchronous Machines in Terms of Efficiency

Permanent Magnet Synchronous Machines find a place in variety of different applications. There is a common need for enhancement of efficiency for electric drives due to general tendency of increase of the energy prices and well-known environmental issues. This paper summarizes available control strategies for an inverse-salient permanent magnet synchronous machine with emphasis on overall efficiency of the electrical drive. The discussed drive is primarily designed for vehicular technology. A mathematical model of the electrical machine including computation of power electronics losses is introduced so that steady-state efficiency at any operational point may be estimated. A part of the process is generation of power loss profiles dependent on reference d- and q- axis currents as controlled variables showing the optimization potential. Efficiency of a drive depends on a selection of control strategy. Therefore, maximum efficiency, maximum torque-per-ampere and Id=0 control strategies among voltage constrained field-weakening strategy are a part of the comprehensive study. A comparison in all considered control strategies in terms of drive efficiency is carried out so that one may track a difference in efficiency for any defined load point.