Assessment of Isolated and Non-Isolated DC-DC Converters for Medium-Voltage PV Applications

The potential of Photovoltaic (PV) panels as a main tool of harnessing solar energy is increasing with the advancements in their power conditioning and conversion stages that vary based on applications. This paper focuses on the conversion of a 22kW PV array output from low-voltage to medium-voltage level (400V to 7kV). This high voltage conversion ratio is difficult to achieve using conventional single-stage DC-DC converters. Thus, different alternatives are proposed and compared here, namely, the Parallel-Input Series-Output (PISO) connection of two different stages using both isolated (full-bridge) and non-isolated DC-DC converters. The converters are compared on the basis of efficiency, footprint, components rating and reliability. Thus, the isolated DC-DC converter system efficiency was estimated at 97%, compared to 93% for the non-isolated system, keeping into account the variations in terms of the filtering capacitor requirements to maintain a constant minimal voltage ripple at the output which is in favor of the non-isolated systems.