MTPA Fitting and Torque Estimation Technique Based on a New Flux-Linkage Model for Interior-Permanent-Magnet Synchronous Machines

The characterization of the interior-permanent-magnet synchronous machine (IPMSM) is limited due to the nonlinearity of the flux-linkage profile by using the conventional motor model. A nonlinear flux-linkage model for the IPMSM with 12 coefficients is proposed in this paper. It can generally be used to estimate the real d-axis flux linkage, q-axis flux linkage, maximum-torque-per-ampere (MTPA) locus, and torque without the information of the machine known, such as the geometry and material of the permanent magnet. The corresponding torque equation and MTPA condition are presented. An optimization problem is formulated to find the appropriate factors for the proposed model based on the measured flux-linkage data at only nine specific operating points. No selection of weight factors is required in the cost function. The desired copper-loss minimization control can be achieved and good torque identification can be implemented in real time. Both simulation and experiment have been conducted to validate the proposed algorithm in motoring and generating modes. Compared with the conventional IPMSM model, the torque estimation accuracy has been significantly improved by considering the saturation and cross-coupling effects in the nonlinear flux-linkage model of the machine.