Injected Grid Current Quality Improvement for Voltage-Controlled Grid-Connected Inverter

Abstract

The injected grid current of the voltage-controlled grid-connected inverter has serious distortion due to the low frequency harmonic components in the output voltage, which is resulted by the dead time of the drive signals of the power switches, and the distortion cannot be eliminated even an output voltage closed-loop is incorporated. This paper introduces a virtual series impedance to increase the output impedance of the grid-connected inverter only at the dominated lower harmonic frequencies, thus the injected grid current quality can be improved and the dynamic performance of the grid-connected inverter is not deteriorated.

Existing System

Droop Control Method.

Proposed System

In order to improve the injected grid current quality further, this paper proposes a virtual series impedance method based on the output voltage close-loop control. The virtual series impedance, which is implemented with the feedback of the injected grid current, is added into the output impedance of the grid-connected inverter, and thus greatly reducing the harmonics in the injected current. Besides, the virtual series impedance is designed to be high only at the dominated lower harmonic frequencies, and it has little impact on the dynamic performance of the grid-connected inverter.

Architecture

Configuration of voltage-controlled grid-connected inverter