A new distributed MPPT technique using buck-only MICs linked with controlled string current

Abstract

A novel idea to realize the distributed maximum power point tracking (DMPPT) control of a photovoltaic system interfaced with an AC grid is proposed. The proposed system is based on the idea of string-connected dc-dc module integrated converters (MICs) that was researched by Walker, Erickson, and others. However, those studies focused on working together with a voltage source inverter (VSI) in a constant DC voltage mode. In addition, all commercial products from companies such as Solar Edge, Solar Magic, and Tigo Energy are working together with a VSI in a constant DC voltage mode. In contrast to past works, the proposed system uses controlled string current with a current source inverter (CSI) to link MICs. As a result, the circuit topology and control scheme of the MICs have been greatly simplified. The authors hope that the proposed system is especially suited for SiC-based CSI applications in the near future. This paper first reviews the conventional control schemes. Then a new MIC-based DMPPT technique is proposed. A simulation study using PSIM is conducted to prove the validity and usefulness of the proposed system. Finally, the successful experimental operation of peak power tracking was confirmed by using two cascaded MICs.