Offline Model Based MTPA Methodology for Optimum Performance of Interior Permanent Magnet Machines over Full Range of Speed and Torque

Abstract

There has been a growing adaptation of Variable Frequency Drives (VFD) for motor applications in all areas. Maximum Torque Per Ampere (MTPA) algorithms are common solutions that aim at achieving efficient operation of drives. This paper presents a novel offline MTPA trajectory generation scheme for an interior permanent magnet (IPM) motor drive. The proposed approach is based on calculating the minimum current possible for every load operating point by solving for polynomial roots of the torque expression in a closed form solution and considers non-linear saturation and cross-coupling properties of the IPM machine. The offline calculation and state logic have been implemented using a model-based design approach and key considerations have been made for efficient execution while minimizing computational resource requirements, thus expanding the deployment scope on a wide range of motor drives including cost sensitive applications. Experimental results obtained on a 3HP IPM motor demonstrate the effectiveness of the proposed scheme in achieving the MTPA control objective while maintaining control stability across all operating regions.