Active Damping Scheme for Leakage Current Reduction in Transformerless Three-phase Grid connected PV

Abstract

This paper analyses the benefits of the active damping applied to transformerless three-phase grid-connected photovoltaic (PV) inverters using modified LCL (MLCL) filter for leakage current reduction. In comparison with passive damping techniques, the active damping can reduce the MLCL filter resonance peaks, improving the dynamic performance of the control system without addition of power losses. Besides these classical advantages, this paper demonstrates that the active damping also contributes for PV leakage current reduction, preserving the high-frequency attenuation of the MLCL filter. Additionally, an active damping for the inverter common-mode circuit is also proposed, reducing the low-frequency leakage current caused by the common-mode signal used to extend the inverter modulation index.

Existing System

Modulation Technique.

Proposed System

This paper proposed an active damping technique applied to transformerless three-phase grid-connected PV inverters that use the MLCL filter for leakage current reduction. Besides the classical advantages of the active damping over the passive damping, this paper demonstrated that it also brings benefits in the leakage current attenuation when it is applied to the MLCL filter. The proposed control system performs the active damping without any damping resistor, improving the inverter efficiency and leakage current attenuation in comparison with a typical passive damping technique.

Architecture

Generic transformerless three-phase inverter connected to the grid through an MLCL filter