Mitigation of Lower Order Harmonics in a Grid-Connected Single-Phase PV Inverter

TLDR

The paper examines a simple single‑phase grid‑connected PV inverter comprising a boost, an inductive‑filter inverter, and a step‑up transformer, noting that while ideal operation avoids lower‑order harmonics, non‑idealities such as transformer core saturation and inverter dead time generate significant lower‑order harmonics in the grid current. The authors propose a novel inverter current control design to mitigate lower‑order harmonics. An adaptive harmonic compensation technique together with a proportional‑resonant‑integral controller is introduced; the PRI controller removes the dc component that would otherwise produce even harmonics, and the interaction dynamics between the PRI controller and the adaptive scheme are analyzed. Experimental validation shows good agreement with theoretical analysis, confirming the effectiveness of the design.

Abstract

In this paper, a simple single-phase grid-connected photovoltaic (PV) inverter topology consisting of a boost section, a low-voltage single-phase inverter with an inductive filter, and a step-up transformer interfacing the grid is considered. Ideally, this topology will not inject any lower order harmonics into the grid due to high-frequency pulse width modulation operation. However, the nonideal factors in the system such as core saturation-induced distorted magnetizing current of the transformer and the dead time of the inverter, etc., contribute to a significant amount of lower order harmonics in the grid current. A novel design of inverter current control that mitigates lower order harmonics is presented in this paper. An adaptive harmonic compensation technique and its design are proposed for the lower order harmonic compensation. In addition, a proportional-resonant-integral (PRI) controller and its design are also proposed. This controller eliminates the dc component in the control system, which introduces even harmonics in the grid current in the topology considered. The dynamics of the system due to the interaction between the PRI controller and the adaptive compensation scheme is also analyzed. The complete design has been validated with experimental results and good agreement with theoretical analysis of the overall system is observed.