Grid-Connected Forward Microinverter With Primary-Parallel Secondary-Series Transformer

This paper presents a primary-parallel secondary-series multicore forward microinverter for photovoltaic ac-module application. The presented microinverter operates with a constant off-time boundary mode control, providing MPPT capability and unity power factor. The proposed multitransformer solution allows using low-profile unitary turns ratio transformers. Therefore, the transformers are better coupled and the overall performance of the microinverter is improved. Due to the multiphase solution, the number of devices increases but the current stress and losses per device are reduced contributing to an easier thermal management. Furthermore, the decoupling capacitor is split among the phases, contributing to a low-profile solution without electrolytic capacitors suitable to be mounted in the frame of a PV module. The proposed solution is compared to the classical parallel-interleaved approach, showing better efficiency in a wide power range and improving the weighted efficiency.

I. Introduction

Traditionally, central inverter technology is used to overcome the low voltage generated by photovoltaic (PV) arrays. However, in residential applications, the energy yield is jeopardized due to mismatches and partial-shading. Distributed maximum power point tracking (DMPPT) architectures, in both dc–dc and dc–ac systems, improve the energy harvesting capability by means of a module-integrated converter [1] , [2]. Despite nonisolated solutions have been presented for both dc–dc optimizers [3] and ac-module applications [4] , the use of a transformer is widespread providing flexibility, an adequate voltage boost and compliance with safety standards [5]– [10].