This paper presents a comprehensive analysis of single-phase full-bridge asymmetrical flying capacitor inverters under distinct capacitor voltage values. The asymmetrical operation is explored in order to increase the number of output levels for the same number of semiconductors. A formation law for the flying capacitors voltages is proposed according to the desired number of output levels. The voltage balance of the flying capacitors is carried out using the charge balance analysis. The modulation strategy is also verified to overcome the inverter unbalance problem. Simulation and experimental results are included to demonstrate the performance of the proposed structures.

Cascaded H-bridge converters are interesting candidates for photovoltaic (PV) and energy storage systems, since PV panels and/or batteries can be directly connected to the input dc-side of each converter module. However, differences in the parameters of the batteries or variable ambient conditions may result in energy imbalances among the power modules. In these cases, conventional modulation strategies will lead to an increased distortion on the converter output voltage. Therefore, this paper proposes a generalized space vector modulation for single-phase cascaded H-bridge converters considering the power processed by each power module and maintaining a low-THD multilevel output voltage waveform. The proposed method improves the converter output voltage harmonic spectrum compared to the conventional phase-shifted modulation strategy in cases of power imbalance among modules. Experimental results are included to demonstrate the performance of the proposed method.

The selection of optimal DC/AC power converter topologies for specific applications is often a time-consuming and complex task, which can lead to suboptimal choices. This paper proposes an AI-assisted methodology to identify the most efficient DC/AC converter based on a set of input design parameters. Separate deep-neural-network-based surrogate models are developed for each considered topology, trained by a large dataset of simulation results obtained from MATLAB/Simulink and PSIM, so that the efficiency of each converter can be determined without performing additional simulations. The proposed methodology allows for quick and accurate efficiency estimation, significantly reducing the analysis time for topology selection. A case study for the two-level converter is also presented, demonstrating that additional parameters, such as the semiconductors junction temperature and output current distortion, can also be predicted using a similar methodology. Results are presented to demonstrate the feasibility of the proposed method.

The Brazilian standard ABNT NBR 16149 defines the tests and procedures for the connection of photovoltaic inverters to the low voltage electrical grid. According to the ABNT NBR 16149, the flicker tests must be performed based on the international standards IEC 61000-3-3, IEC 61000-3-11 and IEC 61000-3-5, wich define a reference impedance for the equipment connection to the low voltage grid. However, the Brazilian grid presents different voltage levels and transformer configurations, so that the reference impedance defined in the international standards are not always compatible with the Brazilian systems. In this sense, this paper proposes a new classification for the inverters, according to the voltage levels and characteristics of the grid. A new reference impedance is also proposed and simulation results are included to demonstrate the impact of this choice for the operation and tests of grid connected inverters.