The analysis of interharmonics generated by VSI-fed adjustable speed drives considering mechanical load fluctuations

The motors with fluctuating mechanical loads exist widely in power systems. Once these motors are connected to power systems through voltage source inverters (VSI), the stator interharmonic currents caused by fluctuating mechanical loads will pass through VSIs and inject into power systems. This paper analyzes the interharmonic currents generated by the VSI-fed adjustable-speed drives (ASD) with fluctuating mechanical loads. The process that the stator interharmonic currents pass through VSIs is analyzed using the modulation theory, and then, the formula is derived to forecast the frequencies of interharmonic currents on supply system side, and finally, its spectrum characteristic is analyzed. Theoretical analysis is verified by simulation results.