Multilevel Current Source Inverters with Phase Shifted Trapezoidal PWM

A 7-level current source inverter (CSI) is proposed for high-power applications. The inverter topology consists of three bridge current source inverters whose outputs are connected in parallel for a large induction motor. The multilevel inverter is fed by an 18-pulse SCR rectifier with three isolated outputs for the reduction of supply-side current THD and the elimination of possible circulating current among the inverters. A phase-shifted trapezoidal PWM (TPWM) scheme is proposed for the inverter to generate multiple current levels. Optimal phase angles are investigated for the reduction of inverter current THD and weighted THD (WTHD). Similar to multilevel voltage source inverters, the multilevel CSI can produce motor-friendly current and voltage waveforms with limited switching frequencies, which is a desirable feature for large motor drives