Bidirectional High-Efficiency Converter with Common-Mode Decoupling for AC and DC Grid Interconnection
Keywords:
Ac-dc converter; common-mode; leakage current; dc microgrids; efficiency; interleaving; silicon carbide (SiC).Abstract
This paper presents an interface ac-dc converter to connect the 380 V bipolar dc
microgrid with the 240 V split-phase single-phase ac utility. The design targets are high
efficiency, leakage current attenuation and symmetric bipolar dc bus generation. A
transformerless two-stage topology is proposed to decouple the common-mode (CM) voltage
between the connected ac and dc systems. The two-stage structure also reduces the required
capacitance in single-phase power conversion by allowing a large voltage ripple on the
intermediate dc-link. Adaptive dc-link voltage control and interleaving of state-of-the-art silicon
carbide (SiC) MOSFETs are adopted to achieve high efficiency. Interleaving angles are
optimized to minimize the total volume of both differential-mode and CM magnetics. An active
CM control method is incorporated to regulate the dc and low-frequency CM voltages on the dc
buses with respect to the ground. The resultant dc bus voltages are rendered symmetric to the
ground, and the leakage current is suppressed. The generated ± 190 V dc bus is suitable for
bipolar 380 V dc power distribution systems. Pluggable phase-leg modules with embedded
driving and protection circuit are designed and tested, based on which a 10 kW all-SiC converter
prototype is built achieving an efficiency > 97 %.
