System-Level Switching-Frequency Trade-Offs in a High-Fundamental-Frequency MW-Class PMSM Drive

While high-speed, high-specific-power permanent-magnet synchronous machines (PMSMs) are critical for emerging aerospace and mobility applications, the existing literature does not provide a comprehensive measurement-based analysis of machine-inverter interactions at megawatt scale. To bridge this gap, this paper presents a system-level, experimentally validated investigation of switching-frequency trade-offs in a 1-MW-class PMSM drive operating at fundamental electrical frequencies up to 1668 Hz. The study quantifies the coupled effects of switching frequency on current total harmonic distortion (THD), torque ripple, machine-side harmonic losses, inverter losses, and passive filter volume under combined efficiency, thermal, and harmonic constraints. Two commercial inverter technologies, a Si IGBT-based inverter and a SiC MOSFET-based inverter, are experimentally evaluated at matched operating points. Measured phase-current waveforms are used in a measurement-driven electromagnetic analysis to isolate additional harmonic losses. To separate switching-frequency effects from semiconductor type, a harmonic synthesis technique is introduced, enabling loss evaluation over a 6-32 kHz switching-frequency range. The results demonstrate that increasing switching frequency significantly reduces current THD, torque ripple, and PWM-induced machine losses. Aggregated system-level loss evaluation across a comprehensive operating map reveals that a static switching frequency is insufficient. Instead, the optimal switching frequency is highly dynamic, exhibiting a proportional relationship with motor speed and an inverse relationship with load torque. For the nominal load, a distinct system-loss optimum emerges around 16-kHz when using SiC technology. Finally, this paper provides practical feasibility maps that highlight the broader impacts of adopting SiC technology for high-speed drives, including minimized system losses and reduced overall system size.