DC power optimizer for PV modules using SEPIC converter

In this paper an instantaneous maximum power extraction scheme is proposed as a PV power optimizer. The presented power harvesting scheme is rely on a weather-based power forecasting model in which the instantaneous value of the maximum power that should be extracted from the individual PV module is computed. The control unit of the proposed dc power optimizer is composed of a PI power controller and a PWM unit driving a SEPIC converter as a power conditioner. The chopper duty cycle is continuously adjusted such that the PV module is forced to operate near the maximum power point that is determined from the online measurements of the meteorological data model. The system is studied under both step down and step up modes of operation permitted by the SEPIC converter. The proposed scheme is investigated under different patterns of solar irradiance. The obtained results indicate both fast transient response and the good accuracy with low computation complexity due to the simple meteorological data model of the PV module. Compared with the commonly used perturb and observe (P&O) technique, the proposed scheme has better performance in terms of lower peak-peak power ripple. However, it has relatively lower tracking efficiency of (1-2)% due to the intentional reduction in the reference power signal to guarantee the fact that the actual harvested PV power can't exceed the reference value determined by the weather based model. The application area of the proposed scheme would be extended from a dc power optimizer for an individual PV to include microgrid applications, where commercially available temperature and solar irradiance transducers can be embedded with the distributed control unit of the SEPIC converter without dramatic increase to the initial cost of the overall system.