Implementation of a modified circuit reconfiguration strategy in high concentration photovoltaic modules under partial shading conditions

Among the available photovoltaic systems, high concentration photovoltaic systems with multi-junction solar cells provide the highest energy conversion efficiency. Unfortunately, the power-voltage characteristics and power output of these systems are greatly affected by the partial shading conditions due to rapid changes in the environmental condition: solar irradiation, wind, and clouds. These nonlinear changes exhibit different maximum power points when subjected to different variations thus increasing the complexity of the solar module arrays. Various strategies have been proposed to address the effects of partial shading conditions. These methods are, however, more complex and costly and thus unsuitable for applications.

An alternative method focusing on the modification of the hardware circuit connection of the photovoltaic arrays have been proposed. This is ascribed to the simple high concentration photovoltaic module architectures comprising of solar cells connected in series with wires and one bypass diode connected in parallel to the individual solar cells that are somewhat easy to reconfigure.  To this end, Mr. Xiang Chen and Mr. Cheng-En Ye (Ph.D. candidate) and led by Professor Dr. Yu-Pei Huang from the National Quemoy University in Taiwan developed a modified circuit reconfiguration method for addressing the partial shading conditions. The work is published in the Solar Energy journal.

First, this method is expected to reduce the cost and complexity by simplifying the hardware switches and control algorithms by implementing the dynamic circuit reconfiguration topology. Next, a string current equalization was performed using the existing switches and connections based on the irradiation estimation method. Finally, the feasibility and practical applicability of the proposed strategy was validated by simulating and evaluating a square and a rectangular based circuit model prototypes with four-cell and six-cell groups respectively.

The simulation and evaluation results showed that the reconfiguration by the modified circuit reconfiguration method significantly improved the output power and efficiency of the two prototype modules. For instance, the average output-power and conversion-efficiency were observed to have respectively improved by 31.07% and 5.00% for the square module and 32.79% and 5.23% for the rectangular module when compared to the original series connection topology. Also, the power-voltage curves of the photovoltaic modules were simplified after reconfiguration. This was attributed to the reduced number of local maximum power points and enhanced global maximum power points. Furthermore, with a small reconfiguration processing time ratio, about 0.06-0.28%, the reliability tests showed a 15% increase in the daily energy harvest for the rectangular module. This novel technique has the advantage of lowering the circuit losses and reducing the costs of hardware and software.

The study by National Quemoy University scientists is the first to demonstrate the implementation of a circuit reconfiguration strategy in high concentration photovoltaic module. This approach simplified the control algorithm and consequently reduced the number of switches thus decreasing the overall implementation cost. Despite the smaller cell groups used in the prototypes, Professor Yu-Pei Huang, the lead and corresponding author observed that the method can be extended to large-scale modules or even implemented with other photovoltaic systems. Altogether, the modified circuit reconfiguration is a promising strategy for the implementation of high-performance photovoltaic solar systems.