Mathematical Expressions and Analysis for Sine-Triangle Clamped PWM Harmonics

Clamped techniques for pulse width modulation (PWM) produce higher AC voltage for a given DC bus and lower losses due to reduced switching. This yields better power quality and higher power density. Harmonic analysis tools are needed to assess power quality of any PWM technique. As fundamental frequencies of power converters such as variable-speed drives are usually changing while source power frequency remains fixed, interharmonic analysis is critical. New industry standards are beginning to impose requirements governing interharmonics. Previously, lumped harmonic analysis of sine-triangle clamped PWM was used, via analysis of time-based simulation, because no final analytical mathematical expressions had been developed to address non-integer carrier frequency ratios to the fundamental frequency. This paper introduces a process for interharmonic evaluation, and derives new analytical expressions for the harmonics of sine-triangle clamped PWM. The new analytical results are validated against the extant simulation-based results.