A Highly Efficient GaN-Based Three-Phase Three-Level Flying Capacitor Inverter With Integrated Triangular Current Mode Control and Clamped Discontinuous Pulsewidth Modulation

Multi-level Flying Capacitor (FC) converters enable the use of lower voltage devices for high voltage systems resulting in high efficiency and high density through the effect of frequency multiplication. Soft-switched integrated Triangular Current Mode (iTCM) based FC inverters can push the efficiency further. iTCM has the advantage of ZVS turn-on like TCM while reducing the ripple on the grid side by inserting an LC-branch between grid-side inductor and the PWM bridge. In this letter, a Gallium Nitride (GaN) based three-phase three-level FC inverter operating in iTCM + Clamped Discontinuous Pulse Width Modulation (DPWM) is presented with the addition of just one LC-branch per phase. The efficiency achieved is 99.16% at 600 V, 11 kW and a minimum inductor current frequency of 300 kHz which is much higher than state-of-the-art two-level converters operating in TCM/ iTCM. As compared to TCM and conventional iTCM, iTCM+DPWM leads to 70% and 25% lower ripple on grid current respectively, thus paving the path for EMI filter size reduction with soft-switched multi-level converters.