On the Inadequacy of IEC 60034-2-3 and IEC 60034-30-2 Standards for Power Losses, Efficiency and Energy Class Evaluation in PWM Multilevel Inverter-Driven PMSM

This work aims to highlight the inadequacy of international standards IEC 60034-2-3 and IEC 60034-30-2 for accurate efficiency, power losses, and efficiency class determination of AC motors fed by multilevel inverters driven with multicarrier PWM strategies. The main motivation of this work stems from the fact that international standards IEC 60034-2-3 and IEC 60034-30-2 prescribe the use of the two-level voltage source inverter for AC motor losses, efficiency, and efficiency classes determination, even for multilevel-inverter-fed AC motor. Therefore, this analysis aims to experimentally demonstrate IEC standards inadequacy, emphasizing the need to update them and provide a comprehensive framework for developing a power measurement procedure, specifically tailored to multilevel inverter-fed AC drives. More specifically, the goal is to support standardization bodies by simplifying their task and enabling IEC standards generalization to almost every multicarrier PWM-controlled multilevel inverter-fed AC drive. To this end, an accurate power loss analysis of an interior permanent magnet synchronous motor fed by a five-level cascaded H-bridge inverter, controlled with several multicarrier PWMs, is carried out. In detail, a precise power analysis in the frequency domain is performed to evaluate the impact of modulation strategies on motor power losses at different operating points in the speed-torque plane in terms of power losses, fundamental, and harmonic power losses. The motor power losses obtained with a five-level cascaded H-bridge multilevel inverter are compared to those obtained with a conventional two-level voltage source inverter, demonstrating that the application of IEC 60034-2-3 and IEC 60034-30-2 provide an underestimated motor energy efficiency class (IE-code).