A novel low voltage ride through control method for current source grid-connected photovoltaic inverters

Abstract

Due to their inherent topology characteristic, current source grid-connected photovoltaic inverters cannot realize low voltage ride through (LVRT) during a serious sag in the grid voltage. Based on mathematical models of three-phase current source grid-connected photovoltaic (PV) inverters, this paper analyzes quantitatively the relationship between steady-state DC-link current and grid voltage, and also derives the steady-state working range of the DC-link current in CSIs. Based on the steady-state working range of the DC-link current and the native characteristics of PV cells, this paper indicates the fundamental reason that three-phase current source inverter cannot realize LVRT. To solve this problem, an improved topology of a current source grid-connected photovoltaic inverter is adopted in this paper, where a chopper circuit is added in the DC link. Meanwhile, a novel control strategy is further proposed to realize LVRT under balanced and unbalanced grid voltage conditions. Finally, the simulation and experiment results verify the effectiveness of the proposed method.