Analytical Formulation of a Maximum Torque per Ampere (MTPA) Technique for SynRMs Considering the Magnetic Saturation

This article proposes an analytical formulation of a maximum torque per ampere (MTPA) technique, accounting for the magnetic saturation of the iron core, specifically developed for synchronous reluctance motors (SynRMs). The proposed MTPA is based on a magnetic saturation model of the SynRM, which has been obtained after simplifying a more complete magnetic model, including also cross-saturation effects. This simplified magnetic model, and consequently the proposed MTPA, can be easily parameterized directly starting from a unique set of tests for the off-line identification of the motor, without the need for any complex, time-consuming, and cumbersome finite-element analysis of the machine under test. The proposed MTPA has been tested experimentally on a suitably developed test set-up. Results obtained with the proposed MTPA have been compared experimentally with both the classic MTPA and the real MTPA. Results clearly show that the proposed technique permits a significant increase of the torque per ampere (TPA) with respect to the case of the classic MTPA, which does not consider magnetic saturation. TPA increase varies from 5% at 3 Nm load to 18% at 12 Nm load. Moreover, the loss of maximum torque, with respect to the real MTPA, obtained at the maximum speed and load torque with the proposed MTPA is about 15%, whereas the loss of maximum torque obtained with the classic MTPA is about 38.5%.