I
N photovoltaic (PV) energy systems, PV modules are often
connected in series for increased string voltage. However,
there is usually mismatch between theI–Vcharacteristics of the
series connected PV modules; this is typically the result of partial shading, manufacturing variability, and thermal gradients.
Since all modules in a series string share the same current, the
string output power may be limited by underperforming modules. A bypass diode is often connected in parallel with each PV
module to mitigate this mismatch and prevent PV hot spotting,
but the efficiency loss is still significant when only a central
converter is used to perform MPPT on the PV string.
To address the mismatch problem, distributed power electronics architectures that perform module-level MPPT, or even
submodule-level MPPT, have been proposed; the two most dominant architectures are DC optimizers [1]–[4], and microinverters [5]–[7], as shown in Fig. 1(a) and (b), respectively. The
major limitation of these two solutions, however, is that the distributed converters are connected in series with the PV modules