Online Optimal Tracking Method for Interior Permanent Magnet Machines With Improved MTPA and MTPV in Whole Speed and Torque Ranges

Abstract

This article proposes a new online optimal tracking method with improved maximum torque per ampere (MTPA) and maximum torque per volt (MTPV) considering magnetic core saturation. The conventional optimality criteria for MTPA and MTPV do not consider magnetic core saturation, and therefore results in deviation from the optimal trajectory especially at higher load currents. This article establishes a mathematical formulation to consider magnetic core saturation in both MTPA and MTPV criteria and proposes corresponding new optimal conditions. The appropriate optimality conditions along with associated constraints form an optimization problem corresponding to an operating region. A simple and straightforward logic sequence proposed in this article identifies the operating regions and initiates corresponding online optimization to find the optimal reference currents at every sampling interval. Moreover, the proposed method ensures that the reference currents are always attainable by considering the inverter nonlinearity, winding resistance, and variation in dc-link voltage into the optimization problem. The proposed online optimal tracking method is successfully implemented in an off-the-shelf motor control unit, and the performances are experimentally validated for wide operating regions.