ABSTRACT:
Parallel operation of
inverter modules is the solution to increase the reliability, efficiency, and
redundancy of inverters in microgrids. Load sharing among inverters in
distributed generators (DGs) is a key issue. This study investigates the
feasibility of power-sharing among parallel DGs using a dual control strategy
in islanded mode of a microgrid. PQ control and droop control techniques are
established to control the microgrid operation. P-f and Q-E droop control is
used to attain real and reactive power sharing. The frequency variation caused
by load change is an issue in droop control strategy whereas the tracking error
of inverter power in PQ control is also a challenge. To address these issues,
two DGs are interfaced with two parallel inverters in an islanded AC microgrid.
PQ control is investigated for controlling the output real and reactive power
of the DGs by assigning their references. The inverter under enhanced droop control
implements power reallocation to restore the frequency among the distributed generators
with predefined droop characteristics. A dual control strategy is proposed for
the AC microgrid under islanded operation without communication link.
Simulation studies are carried out using MATLAB/SIMULINK and the results show the
validity and effective power-sharing performance of the system while
maintaining a stable operation when the microgrid is in islanding mode.
KEYWORDS:
1. Microgrid
2. Inverter parallel operation control strategy
3. Droop control strategy
4. Frequency restore
5. Power sharing
SOFTWARE: MATLAB/SIMULINK
CONCLUSION:
In this paper, the
enhanced droop and PQ control strategies for controlling parallel DGs in
islanding mode of AC micro-grids were investigated to achieve flexible power
regulation. The main advantage of this dual control strategy is to enable
operation without any communication between the parallel DGs. The power
tracking error for PQ control based inverters was investigated and the enhanced
droop control implemented with predefined droop characteristics for power
reallocation was proposed. To improve and restore the frequency, a frequency
restoration scheme (FRS) implemented among the distributed generators was
developed. The proposed droop controller provides stable operating under
different control strategies in islanded operation and the DG voltage can quickly
respond to the required voltage demand. The PQ controller can effectively track
the active and reactive power and the droop control provides voltage control in
islanded mode. The simulation results obtained from MATLAB/SIMULINK verified
the stability of the load voltage and frequency.
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