Hybrid Pulse-Width Modulation Strategy With Reduced High-Frequency Common-Mode Voltage to Lower RMS Motor Leakage Current for a Three-Level Neutral Point Clamped Converter

Due to the capacitive nature of Common-mode impedance, high-frequency Common-mode voltage due to high switching frequency leads to an increase in RMS leakage current, which, in turn, causes higher power loss, Electromagnetic Interferences, and deteriorated harmonic distortion in the three-level Neutral-Point-Clamped converter. Recently-proposed pulse-width modulation type 1 with reduced Common-mode-voltage magnitudes, zero average Common-mode-voltage, and improved harmonic distortion has been presented for the three-level Neutral-Point-Clamped converter. However, the high-frequency Common-mode voltage could be further mitigated by reducing the number of CMV variations. Therefore, this article presents a hybrid pulse-width modulation scheme featuring reduced Common-mode-voltage magnitudes and variations, zero average Common-mode-voltage, and improved harmonic distortion. The Common-mode-voltage variation reduction is realized by re-arranging the order of the switching states in the recently-proposed scheme in a carrier period. The resulting modified sequences type 1 suffer simultaneous switchings between two phase-legs, hence leading to Common-mode-voltage spike due to deadtime. Hence, another type of modified sequences (type 2) is utilized with the modified sequences type 1 and the information of three-phase currents, hence the term “hybrid”. Results under Volt-per-Hertz-2.2KW-rated induction motor with different loading conditions in the Three-Level Neutral-Point-Clamped Converters indicate that at rated frequency of 50Hz, the proposed scheme leads to a noticeable decrease in RMS leakage current while producing similar-to-better harmonic distortion at the expense of slight reduction of the efficiency of a converter as opposed to the recently-proposed Reduced-Common-mode-voltage Pulse-width modulation type 1 with improved switching loss and Phase-Opposition-Disposition-Sinusoidal Pulse-width modulation.