Suppressing EMI Peaks Through Auto-Screening Carrier Phase-Shift Scheme in a PV System Composed of Parallel Single-Phase Inverters

Most photovoltaic (PV) systems are composed of series and parallel inverters. The electromagnetic interference (EMI) mainly comes from the off-on of inverter switches with pulsewidth modulation (PWM). The output EMI peaks of PV systems would increase markedly due to the interference superposition effect caused by parallel inverters, whose carrier initial phases are in phase or close to each other. In this paper, an auto-screening carrier phase-shift scheme is proposed to weaken the superposition effect of EMI peaks and to get the result of reverse offset at its best. In a PV system, through voltage detections and spectrum estimations of each inverter with a series of phase-shift carriers, a best carrier phase of each inverter is obtained automatically to minimize EMI peaks of the PV system. In order to avoid the conflict that the screening processes of two or more inverters are underway at the same time, a specific frequency signal is output temporarily as an occupancy mark in one of the inverters. The feasibility and effectiveness of the proposed scheme are verified by experimental results in a PV system composed of four parallel single-phase inverters.

I. Introduction

Because of goals toward environmental protection, more and more attention is being paid to photovoltaic (PV) power supply as a green energy source [1]. Governments encourage the establishment of a variety of PV systems, including household PV systems.