Reactive Power Control of Critical Mode-Based Soft Switching Modulation for Three-Phase Bidirectional AC-DC Converters
With wide bandgap (WBG) devices, system switching frequency can be pushed to a much higher level in order to achieve higher power density. Since WBG devices have large turn-on energy and extremely small turn-off energy, critical conduction mode (CRM) operation with zero voltage switch (ZVS) soft switching is preferred, so as to achieve high efficiency during high frequency operations.
Based on the novel critical mode-based soft switching modulation proposed in previous work on bidirectional three-phase ac-dc converters under unity power factor conditions, the control concept is extended to bidirectional, non-unity power factor conditions. A generalized critical mode-based soft switching modulation is also proposed which is applicable to both inverter and rectifier modes during unity power factor and non-unity power factor conditions. With this generalized modulation, ZVS soft switching and narrow switching frequency variation ranges are still achievable.
Fig. 1 shows the switching cycle waveforms under a non-unity power factor condition, with the proposed generalized modulation at two arbitrarily selected intervals during CRM operation. This verifies that ZVS soft switching is achieved.