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

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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.

This paper describes the output voltage regulation control for an interleaved connected to a direct current (DC) microgrid considering bidirectional current flows. The proposed controller is based on an interconnection and damping passivity-based control (IDA-PBC) approach with integral action that regulates the output voltage profile at its assigned reference. This approach designs a control law via nonlinear feedback that ensures asymptotic stability in a closed-loop in the sense of Lyapunov. Moreover, the IDA-PBC design adds an integral gain to eliminate the possible tracking errors in steady-state conditions. Numerical simulations in the Piecewise Linear Electrical Circuit Simulation (PLECS) package for MATLAB/Simulink demonstrate that the effectiveness of the proposed controller is assessed and compared with a conventional proportional-integral controller under different scenarios considering strong variations in the current injected/absorbed by the DC microgrid.

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