Hybrid SVM-SOPWM modulation of current-fed three-level inverter for high power application

Current source inverter (CSI) offers key merits of direct output current control, voltage gain operation, current limiting ability, and inherent short-circuit protection. The modulation and control for medium voltage high power application are implemented at low device switching frequency in order to attain high efficiency and to reduce cooling requirements. At low switching frequency operation, the conventional modulation techniques such as space vector modulation (SVM) and sinusoidal pulse width modulation (SPWM) cannot maintain low total harmonic distortion (THD). Synchronous optimal pulse width modulation (SOPWM) is a low frequency modulation technique that offers lower THD without compromising on device switching frequency. However, this technique requires a separate conversion technique for current source converters to incorporate additional switching constraints of CSI. Whereas, the SVM technique directly implements the switching constraints of CSI without any conversion technique and in addition SVM technique provides better dynamic performance compared to low frequency modulation techniques. Hence, the goal of this paper is to propose a hybrid modulation technique that combines the SVM technique and SOPWM technique. Three methods have been proposed for developing hybrid modulation scheme based on SVM and SOPWM. Performance of the proposed hybrid modulation is validated using experimental results.