Online MTPA Tracking for Optimal Performance of IPMSM based Compressor Drives

The efficiency of interior permanent magnet synchronous motors (IPMSM) can be directly influenced by Variable Frequency Drives (VFDs) implementing Maximum Torque Per Ampere (MTPA) algorithms. Model based optimization requires advanced knowledge of machine including non-linear properties which are quite pronounced in IPMSMs. This paper presents a novel online MTPA trajectory seeking scheme which is based on calculating the minimum current possible for every load operating point by dynamically adjusting the current angle during steady state operation. First, an offline MTPA trajectory is derived for the motor using simple datasheet parameters to get a baseline. Second, an online MTPA based on discrete extremum seeking state logic implemented using a model-based design approach is used to seek the least current for a given operating point. Key considerations have been made for efficient execution while minimizing computational resource requirements Experimental results obtained on a 3 HP IPMSM motor demonstrate the effectiveness of the proposed scheme in achieving the MTPA control objective while maintaining control stability across all operating regions.