A Three-Port DC-DC Converter for Solar PV Integration in DC Off-Grid Systems: Design and Control

In dc off-grid systems, each solar photovoltaic (PV) source is conventionally connected in parallel to the dc bus using a second-order boost converter which also performs maximum power point tracking (MPPT). However, this requires multiple dc-dc converters leading to higher component count, lower system efficiency, sub-system interactions, etc. In order to obviate these issues a three-port (double input and single output) fifth-order dc-dc boost converter (FOTPC) is proposed and analyzed, in this paper, for interfacing a couple of solar PV sources with a dc bus in an off-grid systems. The converter has two switches that can be individually controlled to regulate the maximum power point of both solar panels over a wider range of PV voltage and current variation. The operating modes of the converter are described for power extraction from both sources. The paper also presents the steady-state and time-domain analysis of the converter in continuous-conduction mode. Small-signal discrete-time model of FOTPC is developed and used for controller design and stability analysis. The converter operation is validated on a 48 V bus system with nominal power of 200 W.