Reactive Power Control for Single-Phase Grid-Tie Inverters Using Quasi-Sinusoidal Waveform

This paper presents a reactive power control technique for single-phase photovoltaic (PV) inverters, especially unfolding inverters. The proposed system retains the benefit of the unfolding inverters having low material cost and semiconductor losses, and tackles the drawback of the standard unfolding inverter not having capability of reactive power injection. It is important to note that reactive power delivery is mandatory for PV inverters according to the recent announced regulations. The concept is based on changing the shape of the grid current waveform but keeping the same zero crossing points as in the unity power factor condition. The current waveform is governed by real power and reactive power, at the price of an acceptable deformation. The operating principles of the proposed technique and mathematical derivations of the grid current function are provided in this paper. Experimental results in a grid-tie inverter prototype have shown a good agreement with the derived theory, and they confirm the feasibility of using the proposed technique in grid-tie inverters.