A Scalable Unit Differential Power Processing System Design for Photovoltaic Applications

Differential power processing (DPP) systems are able to achieve high system efficiency and maintain maximum power production even under mismatched lighting conditions. However, DPP in large-scale systems has challenges of complicated wire connections and high voltage ratings. The unit DPP structure is introduced to overcome these scalability problems, which consists of bidirectional flyback converters and a bidirectional boost converter to achieve maximum power point operation while minimizing processed power. Both voltage balancing and maximum power point tracking modes are used to effectively control system operation. The unit DPP system and control algorithm are verified through simulation and hardware experimentation. The unit DPP system successfully controls the current of each PV panel to reach its maximum power point. Results shows a 9-10% system efficiency increase compared to series string under uneven lighting conditions.