A novel approach to torque estimation in IPM synchronous motor drives

Environmental-friendly technologies are growing up fast and they are getting more and more attention. In such a scenario, Interior Permanent Magnet (IPM) synchronous motors have all the peculiarities to satisfy the drive efficiency requests. So far, techniques like the Maximum Torque-per-Ampere (MTPA) were a stimulating field of research, because of the great results in term of energy savings. The MTPA locus brings along additional information that is still worth deepening. A proper rearrangement of the torque expression in MTPA condition, obtained by describing the $q$-axis flux linkage by a polynomial approximation, merged with a simple least-square algorithm, returns a fast and accurate on-line estimation of the electromagnetic torque. The effectiveness of the proposed method is proved by a worked out example, based on a IPM drive model fitted with finite-element analysis and experimental measurements, and including motor saturation effects.