Evaluating Losses When Changing Magnetization State in Variable Flux Permanent Magnet Machines

Abstract

This thesis evaluates the losses when changing magnetization state in variable flux permanent magnet machines. A thermal model using a thermal equivalent circuit is established to predict the temperature tendency during magnetization state changing as well. At last, both the results from losses evaluation and thermal equivalent circuit are used to investigate the losses during driving cycle tests. The idea of variable flux permanent magnet synchronous machine is put forward as it has a potential for higher loss reduction compared with conventional permanent magnet synchronous machine. There are three typical methods for magnetization state manipulation: d-axis pulse, straight line stationary frame flux linkage, and loss minimization strategy with closed-loop Je control. A prototype VF-PMSM system is set up for evaluation. The experimental data is processed for FEA to get the loss energy for different components. Then the evaluation of losses with respect to different factors is discussed in detail, including the effect of different manipulation methods, speed, load, magnetization state, and controller gain Kp. A thermal model is established for the prototype VF-PMSM. Parameters for all components in the model are calculated and the model is calibrated using experimental temperature data from high frequency injection operation. Then the model is used to predict the temperature tendency during frequent magnetization/demagnetization operation. At last a Simulink model is established for losses evaluation under driving cycle tests as well as temperature prediction using different operating methods