Inter Harmonic THD Amplification of Voltage Source Converter: Concept and Case Study

In this letter, with the consideration of both PLL and the inter-harmonic voltage perturbation, a technical concept of “inter-harmonic total harmonic distortion (THD) amplification” has been presented, by which a hidden output feature of voltage source converter (VSC) has been unveiled. The phenomenon has been explained in theory that the THD of current is greater than the THD of voltage under the inter-harmonic perturbation during the particular frequency range. The detailed frequency range and boundary characteristics have been given for reference. Both the theoretical analysis and experimental results based on RT-LAB validate the proposed inter-harmonic THD amplification phenomenon. This letter could deepen the understanding of the fundamental THD theory, and provide a new way to evaluate the grid integration performance of VSCs.