Frequency-Coupling Restrained Control of PV Inverters Tied into Weak AC Grid

Under weak AC grid condition, the interaction of the phase-locked loop (PLL), DC-bus voltage control loop and current control loop in a photovoltaic (PV) inverters system may lead to the occurrence of frequency coupling phenomenon, which would bring severe challenge to the stability of the grid-connected system. To address this issue, the mechanism of the frequency coupling in the PV inverters system considering the influence of grid impedance and PLL is firstly analyzed in this paper. And then the equivalent admittance of the photovoltaic inverters system considered the frequency coupling is established. Further, a frequency-coupling restrained control strategy based on phase compensation is put forward to optimize the stability margin given by the Nyquist criterion. Finally, simulation studies are performed to verify the effectiveness of the proposed control.