Unit-Minimum Least Power Point Tracking for the Optimization of Photovoltaic Differentional Power Processing Systems

초록

Recently, differential power processing (DPP) architecture was introduced to enable the maximum power tracking under partial shading conditions. The architecture, however, was found to have more room to optimize the performance by application of an extra extremum-seeking method, so called, Least Power Point Tracking control introduced last year for the first time. Most of the power is processed through the main string converter and only minimal faction of the power which changes depending on the PV-string current is transferred through the low-efficiency bidirectional isolated DPP converters. This paper suggests a second version of LPPT method, called Unit-Minimum power-distributing LPPT. Instead of minimizing the total power of DPPs, the proposed LPPT minimizes the power of DPP converter unit which is the largest among them. Then, the system size and cost can be reduced by the proposed LPPT method which enables the multiple DPP converters to have smaller power capacity and losses than those of the previous LPPT method. The real-time extremum-seeking algorithm employs a perturb-and-observe method which comes from a conventional MPPT one, but the optimization process directs minimal extremity, not maximal. The peak system efficiency achieved with a 400-W prototype DPP system employing the LPPT algorithm is 96.7%. IEEE

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