ABSTRACT:
Distributed generation inverters are
generally operated in parallel with P-f/Q-V and P-V/Q-f droop control strategies.
Due to mismatched resistive and inductive line impedance, power sharing and
output voltage of the parallel DG inverters deviate from the reference value.
This leads to instability in the microgrid system. Adding virtual resistors and
virtual inductors in the control loop of droop controllers improve the power
sharing and stability of operation. But, this leads to voltage drop. Therefore,
an improved P-f/Q-V and P-V/Q-f droop control is proposed. Simulation results
demonstrate that the proposed control and the selection of parameters enhance the
output voltage of inverters.
KEYWORDS:
1.
Distributed generation inverters
2.
Droop control
3.
Microgrid
4.
Output impedance
5.
Virtual resistors
6.
Virtual inductors
SOFTWARE: MATLAB/SIMULINK
Fig.
1. Droop control block diagram.
EXPERIMENTAL RESULTS:
Fig.
2. Parallel inverter output voltage using P-V/Q-f droop control with virtual
resistor under resistive line impedance.
Fig.
3. Active power sharing using secondary control with virtual resistor under
resistive line impedance.
Fig.
4. Reactive power sharing using secondary control with virtual resistor under
resistive line impedance.
Fig.
5. Parallel inverter output frequency using secondary control with virtual
resistor under resistive line impedance.
Fig.
6. Parallel inverter output voltage using secondary control with virtual
resistor under resistive line impedance.
Fig.
7. Active power sharing using P-V/Q-f droop control under inductive line
impedance.
Fig.
8. Reactive power sharing using P-V/Q-f droop control under inductive line
impedance.
Fig.
9. Active power sharing using P-f/Q-V droop control with virtual inductor under
inductive line impedance.
Fig. 10. Reactive
power sharing using P-f/Q-V droop control with virtual inductor under inductive
line impedance.
Fig.
11. Parallel inverter output frequency using P-f/Q-V droop control with virtual
inductor under inductive line impedance.
Fig.
12. Parallel inverter output voltage using P-f/Q-V droop control with virtual
inductor under inductive line impedance.
Fig.
13. Active power sharing using secondary control with virtual inductor under
inductive line impedance.
Fig.
14. Reactive power sharing using secondary control with virtual inductor under
inductive line impedance.
Fig.
15. Parallel inverter output frequency using secondary control with virtual
inductor under inductive line impedance.
Fig.
16. Parallel inverter output voltage using secondary control with virtual
inductor under inductive line impedance.
Fig.
17. Active power sharing using secondary control with different DG ratings
under resistive line impedance.
Fig.
18. Reactive power sharing using secondary control with different DG ratings
under resistive line impedance.
Fig.
19. Parallel inverter output frequency using secondary control with different
DG ratings under resistive line impedance.
Fig.
20. Parallel inverter output voltage using secondary control with different DG
ratings under resistive line impedance.
Fig.
21. Active power sharing using secondary control with different DG ratings
under inductive line impedance.
Fig.
22. Reactive power sharing using secondary control with different DG ratings
under inductive line impedance.
Fig.
23. Parallel inverter output frequency using secondary control with different
DG ratings under inductive line impedance.
Fig.
24. Parallel inverter output voltage using secondary control with different DG
ratings under inductive line impedance.
CONCLUSION:
In this paper, analysis of improved P-f/Q-V
and P-V/Q-f droop control with secondary control for DG parallel inverters in
microgrid is proposed considering line and output impedance. Proportional
integral controller is adopted to ensure accurate tracking of the output
voltage of the inverter to the reference value and the influence of the
controller parameters on the voltage closed loop transfer function and the
equivalent output impedance of the inverter is analyzed. In order to match the
total output impedance of the inverter and line impedance in parallel, the P-V/Q-f
and P-f/Q-V droop control strategy based on the inductive and resistive virtual
impedance is adopted to improve the total output impedance of the inverter
through the virtual impedance. The proposed P-f/Q-V and P-V/Q-f droop control, adaptively
compensates the virtual resistor and inductor voltage drop to improve output
voltage amplitude accuracy to the reference value. Simulation results show the
rationality and effectiveness of the proposed improved control method.
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