Capacitive Virtual Impedance Active Damping Design for Improved Harmonic Rejection in Single-Phase Grid-Tied Converters

This paper presents the use of a virtual impedance active damping (AD) for single-phase grid-tied LCL-type inverters that improves the harmonic rejection in the grid-side current. The AD is achieved through inverter-side current feedback with integral action, emulating the presence of an RC branch in series with the converter-side inductor of the filter, thus providing assistance in the harmonic compensation in order to help comply with power quality standards, such as IEEE 1547 and IEC 61727. The current control uses an alternative structure with grid-side current feedback, based on proportional-resonant controller with harmonic compensation. The virtual impedance and control gains are designed to achieve stability and low total harmonic distortion (THD) in the grid-side current, despite grid parameters variance. The system is analyzed through mathematical modeling and computational simulation. Additionally, experimental results are presented as a form to validate the theory described.