Distributed generation (DG) exploiting the microgrid concept is presented as an effective option for an efficient integration of renewable energy sources into the grid, facilitating intelligent power regulation and energy management to meet the requirement of energy efficiency and the power quality. However, renewable energies present a fluctuating output voltage due to their nature. Thus, the integration of a DC-DC converter with a control stage is necessary to overcome this fluctuation.

The use of conventional DC-DC topologies is widespread. However, the disadvantage of these conventional topologies is that they deliver a restricted output voltage, i.e., they have limited gain due to the parasitic equivalent resistance in the passive components. Moreover, the cancellation of the input current ripple is also limited to a specific point, which is a disadvantage since the renewable energy sources are not stable.

Interest in multilevel power converters has been increased in the last decades due to numerous advantages. Nevertheless, some drawbacks are evident, they involve a higher number of controlled switches and either several isolated dc sources or series connected capacitors.

Consequently, the control complexity increases considerably in view of the fact that more switching devices result in a higher number of possible combinations and the balance of the voltage capacitors has to be guaranteed. In order to accomplish these provisions and achieve low cost, easy control, high efficiency, and high reliability, this paper explores the analysis and control of a modular multilevel DC-DC boost converter based-single switch to interface the PV array with a three phase pulse-width-modulated inverter for smart microgrid application.

The proposed structure uses cascaded capacitor-diode cells to create a multi-level output, which limits voltage constraints on power switches, diodes, and capacitors, thus enabling high amplification ratio. In addition, the converter’s structure benefits from using minimal controlled devices to achieve a high boost ratio, self-balanced output voltage, and unidirectional current. In the studied microgrid the DC/DC converters outputs associated to the PV array and the battery storage are directly linked to the DC-link and AC sources and loads are connected in parallel to the main grid at the AC side. Regarding the control, this conversion structure has twofold requirements that consists in controlling the current injected to the grid and ensures that the DC bus voltage is regulated instantaneously to the command generated by the MPPT function block. An enhanced Variable step size is adopted such that fast tracking speed and high MPPT efficiency are both obtained. Simulation results are provided to verify the validity and performance of the proposed power structure, current control, and MPPT algorithm.

Keywords – multilevel DC-DC boost converter, Photovoltaic, MPPT, microgrid.