Resistive Control for a Photovoltaic Battery Charging System Using a Microcontroller

A new control algorithm has been developed, consisting of a buck-type dc/dc converter, which is used in a parallel-operated photovoltaic battery charging system. From the past research, it has been analyzed that the current loop that is generally used in the parallel operation of the power conditioner has an inherent stability problem in the large-signal domain in the photovoltaic system. The proposed algorithm directly transforms the effective input characteristic of the converter seen by the solar array into a resistive load, which is controlled by a microcontroller-based unit. Thus, the resulting system eliminates the instability associated with the current loop in the photovoltaic system. In addition, it is simple, flexible, and easily expandable. To analyze the effects of the one-sample delay caused by the digital controller, the emulated function in the case of average current mode control is modeled using small-signal approaches, and the design criteria are presented. The experimental results from 180-W prototype hardware show that the proposed algorithm has a simple implementation structure and can stabilize the system in the entire region of the solar array.