Field and circuit combined analysis of permanent magnet synchronous motors

Abstract

A complete procedure has been developed to predict the steady-state and dynamic performances of permanent magnet synchronous machines. The major feature in this study is to combine a finite element analysis with a lumped parameter circuit model in order to provide satisfactory engineering information but at small computational effort. To this end, two co-ordinated stages are involved. One is to develop a unified lumped parameter circuit model applicable for both steady-state and transient analysis. The other stage is to extract individual lumped parameters from finite element solutions based on corresponding equivalent circuits, each with a predetermined topology. -- In this study, static magnetic field calculation is applied to determine the load- dependent direct and quadrature axis reactance parameters Xd, Xq and excitation voltage Eo, in which the effect of the interaction between the d-axis and q-axis quantities is included. Time-varying eddy-current field calculation is used to get starting parameters which serve as the investigation of dynamic behaviour. In order to simplify the time-varying field calculation, time phasor is used to separate the time variable from the field equation based on the introduction of equivalent reluctivity in terms of equivalent magnetic energy. In order to cope with the voltage supply, corresponding finite element formulae are derived with complete elimination of the iterative process for starting current. Due to the availability of the accurate field- based operational parameters, it has become possible to use the lumped parameter circuit model to obtain the complete starting and synchronous performances. -- As an integral part of this study, an effort has been directed to the experimental investigation on the steady-state and dynamic performances. A new load test method is proposed to determine the load dependent parameters Xd, Xq and Eo. In addition, a new microprocessor-based digital torque angle measurement system was designed and built to provide improved accuracy and fast data sampling for measuring and control purposes. At the same time, a scheme for accurately locating the position of zero torque angle is proposed with avoiding access to the internal construction of a machine. -- The proposed techniques have been successfully applied to a l hp laboratory permanent magnet motor. There exists excellent agreement between the simulated and experimental results.