Solar Microconverter Implements Novel MPPT Algorithm

Focus:

Photovoltaic (PV) solar systems usually are deployed as arrays of series-connected PV modules. Optimal energy harvesting from such an array cannot be achieved if its modules are mismatched by design, manufacturing or aging variances, temperature, soiling or shading. Adding a dc-dc power optimizer to each module enables every module to operate at its maximum power point (MPP) independent of the current that loads the array. This article describes operation of a dc-dc power optimizer and a proposed maximum power point tracking (MPPT) algorithm. This algorithm is a variation on the perturb & observe method that uses a variable step size for Iref to overcome limitations of the conventional fixed step size. To avoid tracking errors caused by partial shading of a module, the MPPT is tailored to a specific module topology, i.e. a PV module with a specific number of strings and a corresponding number of bypass diodes (specifically, a 72-cell module.) But this algorithm may be adapted to other module topologies. The dc-dc power optimizer is a digitally controlled buck-boost converter based on the TMS320F28035 microcontroller; the optimzer's operation and performance are described here. Before describing the algorithm, the authors briefly review the common PV module structure and its V-I characteristics.

What you’ll learn:

• How to understand effects of shading on PV module performance
• How to implement a dc-dc power optimizer for solar PV systems
• How to tailor a MPPT algorithm to a specific PV module topology

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Author & Publication:

Richard K. Hester and Dave Freeman, Texas Instruments, Dallas, Texas, How2Power Today, Jun 24 2011

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