Analyzing the optimal matching of dc motors to photovoltaic modules via dc-dc converters

Abstract

Because to the nonlinear behavior of the photovoltaic (PV) cells, dc-dc power converters are added for matching the load to the photovoltaic modules (PVM). In this paper, we use mathematical models in order to examine the behavior of the off-grid photovoltaic system composed by: PV generator, dc-dc converter and dc motor. We compare different converter topologies (step-up, step-down and step-down/step-up) and evaluate the feasibility of being used as interface to attain operation around the maximum power point (MPP). Our analysis found the relationships between the optimal duty ratio and the maximum power, and between the optimal duty ratio and the motor speed; using these relationships, the simplest topology to meet the requirement can be selected as interface. Moreover, a simple but reliable maximum power point tracking (MPPT) method and a controller are implemented on a microcontroller and tested in real weather conditions. The MPPT provides an approximation to the optimal voltage or to the optimal current in a straightforward way, and the controller adjusts the duty ratio of the power converter, improving the matching of the PVM supplying a dc motor, when operation around MPP is obtained.