An Analytical Approach for Characterizing Harmonic and Interharmonic Currents Generated by VSI-Fed Adjustable Speed Drives

Applications of solid-state converters for adjustable speed drives (ASDs) are popular in industrial systems. The ac/dc/ac conversion system, frequently used to provide ac voltages with adjustable frequency/magnitude in the ASDs, consists of a voltage source inverter (VSI) fed by a three-phase diode-bridge rectifier, which generates significant amount of line harmonic and interharmonic currents into the supply system and may cause undesired effects on other power system components. This paper presents an analytical approach for characterizing the current harmonics and interharmonics of the VSI-fed ASD injected into the supply system in steady state, where the circuit models for the rectifier, the dc link, the PWM inverter, and the ac motor are considered in the analysis. The accuracy of the results obtained by the proposed model is demonstrated by comparing with those obtained by using the time-domain simulation tool, Simulink of Matlab, and by laboratory tests. It is shown that the proposed approach is effective to characterize current harmonics and interharmonics generated by the ASD, while the solution accuracy and the computational efficiency are still maintained.