ZVS Turn-on Triangular Current Mode (TCM) Control for Three Phase 2-Level Inverters with Reactive Power Control

Critical conduction mode (CRM)/ Triangular current mode (TCM) control with ZVS turn-on for single phase inverters has led to significant improvement in efficiency at high switching frequencies (>300 kHz). The need to push power converters to high switching frequencies comes from the drive to achieve higher power density as high frequency operation leads to a significant decrease in filter volume which consumes most of the space in power converter systems. With recent advancements in wide bandgap devices' technology, it is possible to operate at high switching frequencies with very low turn-off losses (<;5 W for a 1.2 kW three phase 2-level GaN inverter at 1 MHz switching frequency). A huge increase in power density (from 30 W/in
³
to 80 W/in
³
) is achieved by pushing the switching frequency to MHz range. The turn-on losses in hard switching continuous conduction mode (CCM) though are still significant (>40 W for the above specified operating conditions). Thus, making it necessary to operate the inverter with zero voltage switching (ZVS) turn-on. ZVS turn-on with TCM control for three phase boost PFC has been recently presented, it is shown in this paper how this method can be extended to inverters. However, this new control scheme cannot be just limited to unity power factor operation and reactive power control becomes all the more necessary for inverters as the grid can have reactive loads or reactive power requirements. TCM control with ZVS turn-on in inverter mode for full range of power factor is presented in this paper. It is also shown that even with higher ripple, TCM maintains similar efficiency at 1 MHz as CCM in 50 KHz while achieving 3× power density.