A Soft-Switched High-Frequency Link Single-Stage Three-Phase Inverter for Grid Integration of Utility Scale Renewables

A novel single-stage high-frequency link three-phase (3φ) inverter along with a modulation strategy is presented in this paper. The topology is targeted for grid integration of utility scale renewable and alternative energy sources like solar, fuel cell, and wind, where the power flow is unidirectional (from dc to ac). The primary side converter has a 3φ voltage source inverter (VSI) structure along with an additional half-bridge leg. Sinusoidal pulse width modulation is implemented in the primary side converter. The three legs of the primary side VSI are zero voltage switched (ZVS) for most part of the line cycle. The additional half bridge leg is ZVS over the complete line cycle. The active switches in secondary side converter are line frequency switched and thus results in negligible switching loss. The converter switching process is described in detail to show the soft-switching of the primary side converter using the device capacitances and leakage inductances of the high-frequency transformers (HFTs). The HFT galvanic isolation results in high power density. A 4-kW laboratory scale hardware prototype is built and tested with the proposed modulation strategy. The experimental results are presented to verify the converter operation.