Adaptive control technique for suppression of resonance in grid-connected PV inverters

Grid operating conditions have a significant effect on the harmonic and resonant performance of grid-connected photovoltaic (PV) inverters and changes in grid impedance can cause a notable change in the resonant excitation between the PV inverter and the grid. This study proposes an adaptive control algorithm for grid-connected PV inverters to suppress the resonance condition excited by grid inductance variation, resulting from the dynamic changes in the operating conditions of the distribution network. The causes of resonance between grid-connected PV inverters and the distribution grid are discussed and the design of an active band-pass filter for capturing resonance is described. The proportional gain within the proportional–integral controller is then adaptively controlled in real time to compensate for changes in the grid impedance and suppress resonant excitation while maintaining excellent low-order harmonic performance compared with alternative fixed gain controller techniques, particularly for systems with high values of grid inductance. The performance of the proposed controller is experimentally verified using a 240 V, 2 kVA single-phase grid-connected inverter.