Analysis and control of mismatch power loss in photovoltaic arrays

Abstract

Connecting photovoltaic cells to form an array IN TROD UCTIONhotovoltaic (PV) cells have been developed to the point where they are viable for a range of applications. However, a major problem still affecting the performance and reliability of PV P systems is that of mismatch. Mismatch occurs due to the interconnection of cells with different performance characteristics. This condition results in two detrimental effects: power loss and reliability degradation.When the characteristics of cells within a PV array differ, individual cells may operate suboptimally, causing a reduction in array output power. This is especially the case for cells connected in series with variations in their current outputs. Such a situation may arise simply through shading of a single cell through leaves, bird droppings or dirt falling onto the array. '-' ' Figure 1 shows a typical example of mismatch where a single low current output cell (caused by, say, partial shading) is series connected with four identical cells having normal current outputs. The resultant current-voltage ( I -V ) relationship shows that the current output of the shaded cell significantly limits the current and hence power output of the array. In extreme cases, almost the entire array output can be lost through shading of a single cell. Furthermore, when the array in Figure 1 is short circuited, the low current output cell is severely reverse biased whilst the other cells operate near their maximum

Distributed Maximum Power Point Tracking: Challenges and Commercial Solutions

“…It is well known that, in case of mismatch (due to clouds, shadows, dirtiness, manufacturing tolerances, aging, different orientation of parts of the PV field in the so called Building Integrated Photovoltaic Systems etc. ), the P-V characteristic of the PV field exhibits more than one peak, due to the presence of bypass diodes, and MPPT algorithms can fail [8]- [17]. The failure of such MPPT algorithms is due to the fact that they are not able to avoid that the operating point of the PV source may remain trapped in the neighborhood of a relative maximum power point instead that close to the absolute maximum power point.…”

“…Therefore, since a PV module is equipped with more than one bypass diode, if the module is not uniformly shadowed but, as an example, only one cell is covered by snow or dirt, then the power versus voltage characteristic of the whole PV module may exhibit multiple peaks. In such a case, the MPPT controller of the dc/dc converter associated to such a PV module can lead to a suboptimal operating condition since no MPPT technique is able to correctly face the presence of multiple peaks in the power versus voltage PV characteristic [8]- [17]. Therefore, it is worth noting that DMPPT is fully effective only if each PV module is equipped with as many dc/dc converters as bypass diodes.…”

NMOS-Based Integrated Modular Bypass for Use in Solar Systems (NIMBUS): Intelligent Bypass for Reducing Partial Shading Power Loss in Solar Panel Applications

“…By optimizing the parasitic shunt resistance of the solar cell, the partial shading power loss can be reduced [4]. Normally, we want to maximize this shunt resistance, since it leads to power loss in a fully-irradiated solar panel.…”

Electrical and thermal finite element modeling of arc faults in photovoltaic bypass diodes.

“…The voltage drop depends on the bandgap of the semiconducting material and the current and voltage ratings of the diode. For high-power Si Schottky diodes on the market, the turn-on voltage is often between 0.4 and 0.5 volts [16]. Here we assume the diode voltage drop is 0.45 volts.…”