A q-Z Source-Based Modified Bidirectional Three-Port Converter for Battery-Assisted Solar PV Applications

In this paper, two separate q-Z source-based three-port converters (TPC) with modified bidirectional networks (BDNs) that offer significant voltage gain for photovoltaic (PV)-battery applications are proposed. Both designs allow the converter operation to be carried out in four different modes where the power from primary source can flow to the battery as well as the load and the battery alone can also feed power to the load, at lower duty cycle. The designs are based on a q-Z source converter and use a modified bidirectional path to accommodate the battery port. The main advantage of using one of the two proposed topology is that it provides a common ground for the primary source input (PV), the bidirectional energy storage port, and the output port. In addition to the above mentioned four modes of operation, in the proposed topology, an external switch can be used to charge the battery from the PV source in the absence of the load as well. On the basis of these two distinct advantages, one of the two designs is analyzed in detail. A noncomplex control algorithm is designed to facilitate the battery operation depending upon load power requirement. There are two different duty ratios to control the operation of five MOSFETs to regulate the output voltage. In addition, the converter offers suitable features such as low voltage stress (V ${}_{stress}$) across devices, continuous input current, and common ground (comm.g.) for all three ports, to be used for renewable energy source (RES) applications. The validation of the analytical analysis of the converter is done in a Matlab simulink environment, and the results are presented. For validating the performance of the proposed converter, a 250-V, 450-W prototype is implemented and tested at 10 kHz. The converter in stand-alone mode can attain an efficiency of around 94.5%.