Abstract:
In solar inverter configurations, the central and
string inverters are more popular in micro grid/ utility grid
connected applications. Although string inverters exhibit superior
performance in terms of improved efficiency and reliability
compare to central inverters, but it suffer from the circulating
currents if all string inverter modules connected to common DC
bus. In this work a balanced per-phase sequential controller is
proposed to suppress the circulating currents between the string
inverter modules. The individual phases of the inverter modules
connected at the point of common coupling switched 120°apart
to derive the grid per phase voltage. For an instance to derive
the R-phase grid voltage at 0°, the inverter-1 R-phase would
be switched at 120°and inverter-2 R-phase at 240°connected
together at point of common coupling with the grid. Similar
phase sequential switching with other phases ensures not only
intra phase balance but also inter phase balance at PCC.
The intra phase balance at the PCC confirm the suppressed
circulating currents between the phases and inverter modules.
The proposed per phase sequential operation of the solar inverter
modules exhibit an extra advantage of boosting output voltage
compare to conventional parallel inverter topology. The modular
grid inverter configuration along with the proposed closed loop
control strategy is evaluated analytically and validated through
MATLAB simulations and hardware result
