Analysis of optimal matching between a dc motor and photovoltaic modules via dc-dc power converters

Due to the nonlinear behavior of the photovoltaic (PV) cells, dc-dc power converters are added for matching the load to the photovoltaic generators; thus, maximum power can be reached. In this thesis, mathematical models were used to examine the behavior of the off-grid photovoltaic system composed by: PV generator, dc-dc converter and dc motor. Different converter topologies (step-up, step-down and step-down/step-up) are compared, evaluating their feasibility to be used as interface to attain operation around the maximum power point (MPP). The analysis found the relationships between the optimal duty ratio and the maximum motor speed, which are used to select the simplest topology to meet the requirement as interface. Moreover, several maximum power point tracking (MPPT) methods including model-based MPPT methods and MPPT searching algorithms are implemented on a microcontroller and tested in real weather conditions. MPPT searching algorithms are recommended for real applications, such algorithms do not require tuning due to parameter variations by aging or dusty environment of the PV module and the fluctuation of the PV voltage has little effect on the motor speed.