High-Frequency Harmonics Dispersion for PM Machine Using Discrete Random SVPWM With Narrow Spread Spectrum Range

Spread spectrum range plays a crucial role in random pulse width modulation (RPWM). A narrow-spread spectrum range may result in the unsatisfactory reduction of high-frequency harmonics, whereas an extensive range effectively diminishes these harmonics but introduces significant total harmonic distortion (THD) in phase current and causes torque ripples. This study introduces a discrete random switching frequency space vector pulse width modulation (DRSF-SVPWM) strategy, designed to minimize the peak values of high-frequency harmonics within a narrow frequency spectrum. The key of the proposed method lies in mitigating the average relative change of random numbers by preserving these numbers across consecutive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> carrier periods. A scheme is designed to prove the relationship between the high-frequency harmonic peak at a single frequency and its action time. Additionally, the relationship between the average adjacent changes and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> is investigated. The optimal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> value is determined by combining these two relationships. As a result, the high-frequency harmonics are suppressed to a lower level within a narrow spread spectrum range, and the current THD and torque ripples are not compromised. Simulation and experimental results for a dual three-phase permanent magnet (PM) machine are provided to verify the effectiveness of the proposed method.