ABSTRACT:
This
paper deals with robust control strategy for a distributed generation system
(DGS), which operates in both islanded and grid-connected modes. Generally, in
the low-voltage islanded mode of DGS, the PCC (Point of Common Coupling)
voltages are unbalanced due to the unbalanced load connection. Therefore, in an
islanded mode of DGS, the LSC is controlled using the IPR (Improved
Proportional Resonant) controller to maintain the PCC voltages quality within
the IEEE-1547 standard. Moreover, the DGS is capable to synchronize to the grid
without any transient current. During the change of modes of DGS, large
transients occur in the battery current due to the switching of battery
control. This problem is resolved by the presented bidirectional DC-DC converter
control strategy and robust ILQSOGI (Inner Loop Quadrature Second Order
Generalized Integrator) based PLL. The effectiveness of this DGS control
strategy is verified by the corresponding MATLAB/Simulink platform under load
unbalance, solar irradiance changes and during mode of switching. Moreover, the
simulation results are validated using the test results and show the robustness
of the control strategy during abnormal grid voltage condition.
KEYWORDS:
1. Solar Photovoltaic Array
2. Power Quality
3. Bidirectional DC-DC Converter
4. Load Side Converter (LSC) and Machine Side Converter (MSC)
SOFTWARE: MATLAB/SIMULINK
SCHEMATIC DIAGRAM:
Fig.1 Proposed DGS configuration
EXPECTED SIMULATION RESULTS:
Fig.
2 Performance of DGS during mode of switching from IMS to GCM
Fig.
3 Power quality indices of DGS in GCM (a) harmonic spectrum of ig (b) harmonic
spectrum of iL
Fig.
4 Performance of BDC control under mode of transition (a) without and with BDC
control under grid connection (b) without and with BDC control under grid disconnection.
Fig.
5 Comparison of load voltage waveforms (a) with proposed islanded control
technique (b) conventional islanded PI control techniq
Fig.
6 Comparison of load voltage THD (a) with proposed islanded control technique
(b) conventional islanded PI control technique
Fig. 7 Performance of DGS (a) solar and wind power variation in IMS (b) at unbalanced load condition in IS mode
CONCLUSION:
The
proposed islanded control technique has used the positive sequence load current
components with PR control, which has improved the load voltage quality under
unbalanced nonlinear load condition and the results have proven the robustness
of control technique in islanded mode of DGS. Simulated results have shown the
significant difference in PCC load voltage quality using conventional and
proposed islanded control technique. Moreover, simulated results have proven
the good load voltage quality under unbalanced nonlinear load condition and the
range of load voltage quality lies under the IEEE-1547.4 standard. Experimental
results show the robustness of the control strategy, which is capable to
operate the DGS in different modes such as in grid connected mode and islanded
mode. Moreover, the transient free mode change is also presented through test
results. The qualities of PCC voltages and currents are also maintained under
the IEEE-1547 standard, in the grid connected mode, an islanded mode and during
mode transitions. Test results have presented the performance of DGS under
different dynamic conditions and validated the robustness and effectiveness of
control schemes. Test results have also shown the effectiveness of feed-forward
term in grid connected mode and the smooth operation of grid connected mode
under battery disconnection.
REFERENCES:
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[2] M. Savaghebi, A. Jalilian, J. C. Vasquez and J. M. Guerrero, “Secondary Control Scheme for Voltage Unbalance Compensation in an Islanded Droop-Controlled Microgrid,” IEEE Trans. Smart Grid, vol. 3, no. 2, pp. 797-807, June 2012.
[3] IEEE Guide for Design, Operation, and Integration of Distributed Resource Island Systems with Electric Power Systems, IEEE Standard
[4] Bhutto, Ghullam and Bak, C.L. and Ali, Ehsan, “Controlled Operation of the Islanded Portion of the International Council on Large Electric Systems (CIGRE) Low Voltage Dist. Network”, Energies, 20.17.
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