Feed-forward decoupling control to enhance robust stability of PV inverter connected to a weak grid

Abstract

This paper presents a feed-forward decoupling control method to enhance the stability of a photovoltaic (PV) inverter connected to a weak grid. As the grid weakens, the point of common coupling (PCC) voltage becomes sensitive to the active power. This increases the coupling effects between control loops, Phase-Locked Loop (PLL) and grid dynamics, which deteriorate system stability. Therefore, in this paper, a decoupling control method is proposed in which the reference active current obtained by regulating the DC-link voltage to its reference value is feed-forwarded to modulate the reactive current reference generated by regulating the PCC voltage to its predefined value. As result, the robust performance of the PV inverter connected to a weak grid has been yielded, where the inverter stability is maintained for both wider PLL bandwidth and high grid impedance. Based on open-loop bode plot and closed-loop eigenvalues of the DC-link voltage control (DVC) loop, a stability analysis of the proposed control method and the conventional vector control method has been performed. Then, the proposed method is verified through simulation results obtained by PLECS.