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A High-Efficiency Interleaved Single-Phase AC-DC Converter with Common-Mode Voltage Regulation for 380 V DC Microgrids

Year: 2018 | Author: Fang Chen | Paper: D4.9
Image of two-stage bidirectional single-phase ac-dc converter with common-mode decoupling, conceptual schematic, and complete interleaved schematic.
Fig. 1. Two-stage bidirectional single-phase ac-dc converter with common-mode decoupling (a) conceptual schematic, and (b) complete interleaved schematic.
Due to the higher efficiency and reliability associated with ac distribution, dc power distribution has become an attractive solution to connect renewable power sources and energy storage. Dc microgrids can be connected to the ac utility through grid-interface converters and exchange only the net energy. The grid-interface converter is expected to fulfill the following functions:

  1. Dynamic decoupling between ac and dc systems.; The transient on one side should not impact the power quality on the other side.

  2. Bidirectional power flow.

  3. Current limiting if the ac or dc side is shorted.

  4. High-efficiency and high-power density.

  5. Electromagnetic interference (EMI) compliance at both ac and dc interfaces.

  6. Leakage current control.

To connect ac and dc grids, the grounding scheme is critical. To decouple the common mode (CM) voltages between the connected ac and dc systems, a two-stage symmetric converter topology is needed, as shown in Fig. 1. The developed 10 kW two-stage ac-/dc power converter is shown in Fig. 2.

A two-stage converter, together with its filter and control loop design, are discussed as a means to decouple the CM voltage when a dc micro grid and ac utility are connected. To achieve high efficiency, interleaved two-level full-bridge topology with silicon-carbide (SiC) metal-oxide semiconductor field-effect transistors (MOSFETs) working at 40 kHz switching frequency is optimal. A pluggable phase leg module with embedded protection is designed for scalability. The volt-second applied on each inductive component is analyzed to estimate the component size and assist in the magnetics design. A 10 kW converter prototype is built, and achieves an efficiency higher than 97 percent. The dc bus to ground voltage is controlled by a CM voltage controller of the full-bridge dc-dc stage. The resultant dc bus voltages are symmetrical to the ground without any ripple.

Image of 10 kW two-stage ac-dc power converter.
Fig. 2. 10 kW two-stage ac-dc power converter.

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