PhD student Shibin Qin with advisor R. Pilawa-Podgurski
Single-phase grid-tied converters (single-phase ac-to-dc, or dc-to-single-phase-ac) have wide applications in both energy harvesting (such as solar micro-inverters) and consumption (such as chargers for electric vehicles). High-efficiency and high-power-density converters are the most critical features for many of these applications.
In this research, a power factor correction (PFC) frontend is developed based on a 7-level flying capacitor multilevel topology to improve the power density by an order of magnitude, compared to conventional PFC, while maintaining comparable power density. The topology leverages a frequency-multiplying effect that enables very high effective frequency on the filter inductor with moderate transistor switching frequency. It features low transistor voltage stress, high efficiency and a very small filter inductor to achieve high power density, while the small inductance imposes unique challenges to the PFC control operation. These challenges have been met with advanced digital control techniques implemented in the TI C2000 microcontroller. A hardware prototype, as shown in Figure 14, was built to demonstrate the high power density. This PFC converter, together with the active energy buffer developed in previous research, form a complete high power density solution for grid-connected power supply. This research is supported by Texas Instruments.