load sharing improvement between parallel- connected inverter based dgs using a ga based...
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By: Mahdi Zolfaghari
Load Sharing Improvement Between Parallel-Connected Inverter based DGs Using a
GA based Optimization Control Strategy in
Microgrids
Aims of The PaperStudying the load sharing problem among
DGs in microgrid
Analysis of the effects of changing in the line impedance on the load sharing between DGs
Introducing an improvement to the commonly used IACS(instantaneous average current control scheme)
Problem Statements
• A desired load sharing is an important challenge with the future microgrids
• Undesired load sharing results in:A circulating current among DGsUnbalanced sharing of active and reactive
powers between DGsVoltage drop and power loss
Related Works
• In [2], a master-slave control approach was proposed.
The main disadvantage of this method is its poor reliability
• In [3,4], a strategy based on the conventional voltage and frequency droop
a well-known limitation, in which an inherent tradeoff exists between the output voltage regulation and power sharing accuracy.
Contribution of the paper
• Flowchart of optimizing the OPI using GASTART
Create initial population
Applied in concentration
control
Evaluate objective
function, ITAE
Fitness selection
Is termination criteria reached?
Create new population by reproduction,
crossover, mutation
Optimal PI parameters
End
Yes
No
t
dtvtITAE0 0
Optimization index:
Simulation Results• Case I: the resistance of transmission line 1, is reduced from
0.8Ω to 0Ω in 0.1Ω steps
Simulation Results• Case II: The inductance of transmission line 2 is increased
from 0mH to 0.5mH in 0.1mH steps
Discussion• The parameters of the PI controller were tuned by
conventional Zeigler-Nichols method and obtained as: Kp=3.7, Ki=1.8
• For the two cases, the load is considered with lagging power factor as 1000 W, 400 VAr and the voltage at load bus is 230 V, 50 Hz and the DC side voltage of inverter is 400 V.
• For case I, circulating current by using the PI controller is 0.3A whereas it is reduced to 0.2 A by using the OPI
• For case II, the PI controller reduces the circulating current to 0.4 A while the OPI reduces to 0.18 A. The reactive power difference: is 280 VAr when using PI and it is 100 VAr by implementing OPI
Conclusiono Microgrids are an essential parts of future smart gridso A desired load sharing between DGs is in important
challengeo This work presented an improvement to the IACS
strategyo The parameters of the controller were optimally tuned
using GAo The simulation results indicated the effectiveness of
the controller
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