Özet:
The proposed study deals with modeling and
implementation of a multilevel string inverter with non-isolated
dc-dc converter design. The modeled system is intended to be
used for solar applications that the photovoltaic panels are
connected in string structure. However, the dc-dc converter and
multilevel inverter are capable to be used in distributed energy
generation applications owing to the proposed control
infrastructure. The entire design includes dual buck converter at
the dc coupling input where both of the converters
simultaneously operate to regulate photovoltaic string voltages.
Each dc converter is capable to manage a string comprised of two
photovoltaic arrays at the input. The maximum power of each
solar array is allowed to be 1.2 kWp while the maximum value of
total input power is limited to 4.8 kWp regarding to the related
international standards such as AS4777-2013, IEC62109, and
IEC61727. The output voltages of dc converters are set to 120V
by the proportional-integral controller and are coupled over dc
busbar to supply 9-level string inverter. The multilevel string
inverter is comprised of two H-bridges in symmetrical topology
where it is arranged according to regular 5-level symmetrical
inverter. Furthermore, the regular sinusoidal pulse width
modulator is enhanced to increase voltage level of inverter to nine
instead of regular 5-level output. The inverter provides unity
power factor with 0.63% total harmonic distortion ratio.