Many kinds of residential PV systems have been developed, mounted
and increasing on a lot of houses. These systems are generally classified
into two types, one of them has DC (direct current) wiring and one
inverter, the other one called AC module has AC (alternative current)
wiring and a module integrated converter (MIC) behind each PV module.
In Japan, almost all of the roof top systems belong to the former
one. In this type, DC wires of PV modules are connected in series
and/or in parallel to a power conditioner with 3 kW to 4 kW capacities.
It is known that partially shaded modules perform as resistance component,
which reduce the total output power of the series/parallel connected
modules. The same is applied to another case in which several PV modules
have different characteristics by means of the difference of irradiation
and so on. Residential areas are usually bristling with buildings
and plants, which often cast their shadows on roof mounted PV arrays.
Furthermore, roofs of residential houses are in various shapes and
sizes, therefore the generated power from each PV module is different
by the part on a roof. Against these problems, it is said that AC
module is effective, which tracks the maximum power operating point
by each PV module.