Photovoltaic system with bumpless transfer between grid-connected and stand-alone modes

This paper discuses a Quasi-Uninterrupted Power Supply (Q-UPS) with photovoltaic (PV) grid-connected system to increase energy production for local consumption. The purpose of this system is to supply the load when connecting to the utility grid, but also when a power outage occurs. During normal operating mode, the PV power is driven to the grid and the load just consume its own power. Therefore, the PV always operates at the Maximum Power Point (MPP) and in this mode, a current controller is used. During the fault, the PV supplies the load, while the PV power is higher than the load power, although it does not necessarily operates at the MPP and in this mode, a voltage controller is used. In addition, to provide smooth transition when changing the controllers, a bumpless scheme was implemented. Thus, a seamless transition is achieved in any quarter of the sine waveform, not only at the zero-crossing.