Multifunctional PV Converter for Uninterrupted Power Supply

Multifunctional converters or hybrid inverters are usually connected to the utility grid and can operate on islanded mode due to their association with batteries. The PV systems are commonly implemented using two stages of power processing. The first stage is a DC-DC converter and the second stage is a DC-AC converter. In multifunctional converters, bidirectional operation is necessary to allow the charge and discharge of the battery banks using a single converter. Therefore, these systems need three power processing stages with coordinated control. Battery banks are commonly applied in uninterruptible power supplies (UPS) in order to supply critical loads. However, in PV systems several modes of operation are possible, including the charge/discharge of the batteries and islanded mode. When supplying critical loads, there is a critical situation, related to the transitions between on-grid and off-grid modes, in this paper, the control of this modes are explored as a means to perform uninterrupted power supply to the loads with fast response. For this, the control schemes of on-grid and off-grid modes are detailed. To corroborate this purpose, hardware-in-the-loop results are presented.