In this study, a new isolated bidirectional DC-to-three-phase AC converter for integration of renewable energy sources to the electric grid is presented. The main features of this topology are galvanic isolation, capability to control the power flow bidirectionally, soft switching, unit power factor under open-loop control and also allow step up and step down the voltage. Its operation principle is described and a modulation strategy is proposed, which allows to control the power flow according to the requirements of the load and to operate with minimum switching losses owing to the soft switching. The results revealed the feasibility of the proposal with a THD i of the AC current waveforms below 5% and the power factor above 0.98. (a) With a low-frequency transformer with an AC-DC converter, (b) With an AC-DC converter and an isolated DC-DC converter, (c) With an isolated AC-DC converter

Different power converter topologies are used to perform the energy exchange between an AC grid and a DC source belonging to a hybrid electric micro-grid. A single-phase single-stage isolated AC-DC power converter is one of them. Moreover, this power converter can operate under different modulation strategies. The phase-shift modulation (PSM) strategy is capable of varying the phase between the voltages applied to the high-frequency transformer terminals of the power converter in order to control the energy flow in both directions. Based on the PSM strategy, this study presents a novel modified PSM strategy capable of controlling the power flow in both directions and obtaining a current with low total harmonic distortion and a power factor close to 1 for the entire operating range on the AC side. Considering the novel modulation strategy to be proposed, a comparison of three PSM-based modulation strategies was carried out taking into account the total harmonic distortion of current injected into the AC grid, the power factor and the average power transferred. A theoretical analysis was carried out and the results obtained were validated by means of experimental results.

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