This article proposes a 27-level asymmetric cascade H-bridge multilevel topology for photovoltaic applications, which considers a predictive control strategy that allows minimization of the commutations of the converter. This proposal ensures a highly sinusoidal and stable photovoltaic injection when there are solar irradiance disturbances, generating a low distortion in the current waveform and low switching losses. To validate the performance of the control and the proposed topology, the dynamic model of the alternating current (AC) and direct current (DC) side system is first obtained, which is checked by computational simulations. Subsequently, the implementation of a master–slave control is carried out, focused on the control of DC voltage and AC current. The proposal is simulated, and the total harmonic distortion (THD) is obtained in the voltage and current waveforms. Undesired commutations, typical of the predictive control, are eliminated in the AC voltage waveform, and a proper DC voltage tracking is achieved for the high-power cell. In order to demonstrate the performance of the proposed control strategy, a low-power proof-of-concept prototype is implemented, in which the energy is injected to the grid, under the event of solar irradiance disturbances (with DC control).Then, the undesired switching in the main cell is eliminated, generating THDs in the voltage and current signal of 7.76% and 2.65%, respectively.

Abstract-The massive penetration of renewable energy sources in the utility grid has emerged as the solution to obtain clean energy in modern electric systems, which are gradually replacing their generators that produce CO2 emissions to achieve a sustainable growing. Power electronics is quite relevant in the deep penetration of renewable energy, because the use of such equipment is mandatory to integrate these new resources with the existing facilities. In order to reach higher power ranges, multilevel topologies are the state-of-the-art solution, due to the limited rating of the actual semiconductor devices. Furthermore, latest trends show that asymmetric multilevel configurations are an attractive technology to connect directly the power converters to the grid. This paper analyze the photovoltaic energy injection to microgrids using a hybrid approach that mixes the existing topologies: string, multistring and central inverter to implement an asymmetric structure that generate highly sinusoidal resulting waveforms. This document includes a simple analysis of the proposed configuration and highlights the advantages of using an asymmetric converter, supported with stationary and dynamic simulated results.

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