Differential and Common Mode Active Resonance Damping Control for Shunt-less LCL Filter Based Grid-Connected PV Inverters

This paper presents a generalized Differential Mode (DM) and Common Mode (CM) active resonance damping control scheme for grid-connected Photovoltaic (PV) inverters that are based on a shunt-less LCL filter. The proposed technique is useful for applications where the utility grid is weak. This is because weak grid’s large stray inductance challenges the DM control stability. Likewise, it will be indicated in this work that weak grid’s improperly designed ground resistance influences the CM control stability. Thereby, this paper develops an active resonance damping scheme for both the DM and CM controls. The developed scheme requires sensing the filter capacitors’ DM and CM currents. Then, these supplementary parameters are fed-back in their respective control loop with a proportional gain. This scheme emulates a virtual damping resistor in-parallel with the filter capacitors in each control mode. The stability achievement of the modified control system is examined using Pole-Zero plots. Also, the theoretical analyses are confirmed on a 10 kW PV system that is synchronized with a 240VRMS/50Hz weak grid.