Stability Problems of Photovoltaic (PV) Inverter in Weak Grid: A Review

Photovoltaic (PV) power generation, as one important part of renewable energy, has been greatly developed in recent years. The stability of PV inverters is very important for the normal operation of PV systems. However, most PV systems, especially the large PV plants, locate in rural areas. The corresponding equivalent grid impedance is rather large and easy to lead to stability problems of grid-connected inverters and many researches have been done focusing on the stability problems. In this study, a survey of stability problems of PV inverters on weak grid condition is given. The stability problems are mainly divided into two parts, i.e. the control loops instability and inverter output voltage instability. The control loops cover the current loop and dc voltage loop. The output voltage instability refers to the voltage phasors relationship and the application of reactive power compensation. The non-linear parts of inverter dead-time, digital control delay, and phase-locked loop are explored. Future trends and challenges are given.