V. Fernao Pires’s research while affiliated with Instituto Superior Técnico and other places

As the electricity landscape evolves towards greater penetration of renewable energy, voltage source inverters (VSIs) have established themselves as the key power electronics interface between distributed energy resources and the electrical power distribution in modern nanogrids (nGs), capable of working as grid‐following (GFL) converters during grid‐connected operation and as grid‐forming (GFM) converters when islanded. As a relatively recent advanced inverter topology, the three‐level T‐type quasi‐impedance source inverter (3L T‐Type qZSI) offers the improved harmonic distortion and lower switching losses characteristic of the three‐level T‐type topology, combined with the boosting capability of the quasi‐impedance source network, all within a single power stage. Despite the many benefits of this topology, neither the use of wide bandgap semiconductors for the power converter design nor the study of its feasibility in an islanded ac nG has been conducted. In this paper, a full silicon carbide (SiC) 3L T‐Type qZSI experimental prototype was designed, assembled and tested in the context of an islanded nG with a hierarchical GFM control structure operating at a high switching frequency of 50 kHz. The performance of the 3L T‐Type qZSI prototype and the overall nG system was verified by simulation and experimentally.

Wind and solar renewable energy sources (RES) have been fundamental in reducing carbon emissions in electrical energy systems. However, when integrated into low voltage grids, some problems can arise due to the high number of single-phase loads. This situation often leads to unbalanced loads, which can result in increased losses or even under- or over-voltages in one of the phases. This issue is even more critical in the context of isolated microgrids. Therefore, this paper introduces a novel control system for a grid-connected photovoltaic (PV) generation setup based on a dual three-phase four-leg multilevel inverter. This power converter topology, comprising two four-leg two-level three-phase inverters, connects two PV arrays to a three-phase transformer with four wires which in turn connects to a grid. This arrangement is designed to inject PV-generated power into the low voltage (LV) grid, providing support for unbalanced loads. A backstepping method is derived to predict the optimum converter voltage and near optimum vector to control the load currents. As only one voltage prediction is needed a fast controller is obtained even if the converter has high number of voltage vectors. This backstepping prediction increases the speed of choosing the converter vector, allowing the control of the grid currents injected under both balanced and unbalanced conditions, while also maintaining balance of the capacitor DC voltages in RES. Experimental tests were conducted using a laboratory prototype to evaluate the backstepping prediction performance applied to the proposed PV generation system.

The nine-switch inverter is considered as a very interesting solution for three-phase dual output applications, such as dual three-phase or six-phase motor drive systems. The main advantage of this approach is a converter topology with a reduced number of power semiconductors. However, the AC output voltages are limited to only two levels. This work proposes a new inverter topology for dual three-phase or six-phase motor drive systems with multilevel output characteristics. The proposed topology is based on two isolated inverters, but the number of legs is reduced from six to three. This structure creates a modular multilevel inverter with a high number of voltage levels, while using a comparatively smaller number of power semiconductors. A modulation strategy, associated with the proposed topology, is presented to ensure multilevel operation. The proposed topology and modulation strategy will be tested firstly, through a simulation in Matlab/Simulink, and then, by laboratory tests, using an experimental prototype. The obtained results show a good agreement between simulations and experiments both confirming the theoretical studies.

This paper presents a new high-voltage gain single-phase seven-level Boost inverter topology with reduced harmonic distortion. The proposed solution introduces a transformerless multilevel voltage source inverter with reduced number of passive and active power components using only a single input DC power source. The maximum voltage gain is three times higher than the input power source. The circuit is composed by a double boost controlled cell using a single power device where both inductors suppress the capacitors current charge spikes. The proposed topology is verified under different conditions, and the some simulation and experimental results are presented, considering a 300 W laboratory prototype model.

Over the last few years, there has been a high demand for new or improved isolated DC-DC to fulfill requirements of applications related with RES. In this context, this paper introduces a new isolated DC-DC converter, for use in renewable energy applications. The topology proposed contains an Active quasi-switched Boost Three-Level T-type DC-DC converter with continuous input current at the converter input side, connected to a high-frequency step-up isolation transformer, and a voltage doubler rectifier (VDR) on the output side. The steady-state analysis of the proposed converter is presented and discussed. Simulation results are presented to verify the theory and performance of the converter.