A cost-effective power ramp-rate control strategy for single-phase two-stage grid-connected photovoltaic systems

In the case of a wide-scale adoption of grid-connected Photovoltaic (PV) systems, more fluctuated power will be injected into the grid due to the intermittency of solar PV energy. A sudden change in the PV power can potentially induce grid voltage fluctuations, and thus challenge the stability of the grid. Hence, this sudden active power change resulting in a large power ramp-rate should be avoided in practice. In fact, some grid regulations also released strict rules on active power ramp-rates for PV systems. This paper proposes a cost-effective control strategy to limit the power ramp-rate for two-stage grid-connected PV systems. The main concept of the proposed scheme is to modify the maximum power point tracking algorithm in such a way to regulate the PV power at the left side of the maximum power point curve. As a consequence, the power ramprate can be controlled according to the set-point. Experiments conducted on a 3-kW single-phase two-stage grid-connected PV system have verified that the proposed solution can accomplish fast dynamics, high accuracy, and high robustness in the power ramp-rate control for PV systems.