ABSTRACT:
This study proposes a two-layer hierarchical control
to actualize optimal total harmonic distortion (THD) compensation in different
buses of parallel-connected inverters in islanded microgrids which had not been
studied so far. The proposed secondary layer is used to realize THD
compensation of sensitive load bus (SLB) and make distributed generators (DGs) distribute
the compensating efforts between them according to their rated capacity. It is
noteworthy that improving THD at the SLB can lead to an increase in THD at
local buses and/or DG terminals. Although the THD limitations of these buses
are not as strict as the THD limitation of SLB, it is necessary to control them
within their allowed range. This important problem is not well studied in the
literature. A novel complementary part is designed and added to the secondary
control to tune the compensation portion of each DG while the THD limitations
in DG terminals and local buses are considered. The proposed method actualizes a
multi-level voltage quality control in multi-bus islanded microgrids with
parallel DGs through a simple yet effective solution. Furthermore, considering
the DGs peak current limitation is added to the controller and a method for
calculating this peak value is proposed.
SOFTWARE:
MATLAB/SIMULINK
CONCLUSION:
A
new two-level control hierarchy structure ,which had not been studied before,
is proposed in this study to actualise the optimal compensation of voltage
harmonics in islanded microgrids without any additional equipment installation.
The primary layer controls the voltage and frequency and also the FPS power
sharing. The secondary level controls the THD of SLB. Improving THD at the SLB
can lead to an increase in THD at local buses and/or DG terminals. Although the
THD limitations of these buses are not as strict as the THD limitation of SLB,
it is necessary to control them within their allowed range. A complementary
part is designed and added to the secondary control in order to tune the
compensation efforts of each DG unit while considering the THD limitations in DG
terminals and local buses. Furthermore, considering the DGs peak current
limitation is added to the controller and a method for calculating this peak
value is proposed. The proposed control structure realises a
multi-power-quality level control for islanded microgrids with multi-bus and
parallel DGs through a simple yet effective solution.
The
design of the proposed control is very simple and it is not needed to have the
microgrid parameters and structure. Therefore, it would be more functional and
also the plug & play ability of DGs would be reserved as well. An example
system is modeled and simulated. Simulation and comparison results are
presented to demonstrate its effectiveness.
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