ABSTRACT:
This paper presents a unified control strategy that enables
both islanded and grid-tied operation of three-phase inverter in distributed
generation (DG), with no need for switching between two corresponding
controllers or critical islanding detection. The proposed control strategy
composes of an inner inductor current loop, and a novel voltage loop in the synchronous
reference frame (SRF). The inverter is regulated as a current source just by
the inner inductor current loop in grid-tied operation, and the voltage
controller is automatically activated to regulate the load voltage upon the
occurrence of islanding. Furthermore, the waveforms of the grid current in
grid-tied mode and the load voltage in islanding mode are distorted under nonlinear
local load with the conventional strategy. And this issue is addressed by
proposing a unified load current feed forward in the paper. Additionally, the
paper presents the detailed analysis and the parameter design of the control
strategy. Finally, the effectiveness of the proposed control strategy is
validated by the simulation and experimental results.
KEYWORDS:
1.
Distributed
generation
2.
Three-phase
inverter
3.
Islanding
4.
Unified
control
5.
Seamless
transfer
6.
Load current
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1 Schematic diagram of the distributed generzation based on the proposed
control strategy.
Fig.
2 Bode plot of the transfer function from load current to grid current with
and
without the load current feedforward, when DG operates in grid-tied
mode.
Fig.
3 Simulation waveforms of load voltage vCa, grid current iga and
inductor
current
iLa when DG is in grid-tied mode under condition of the step down of
the
grid current reference from 9A to 5A with: (a) conventional voltage mode
control,
and (b) proposed unified control strategy.
Fig.
4 Simulation waveforms of load voltage vCa, grid current iga and
inductor
current
iLa when DG is transferred from grid-tied mode to islanded mode with:
(a)
conventional hybrid voltage and current mode control, and (b) proposed
unified
control strategy.
CONCLUSION:
A
unified control strategy is proposed for three-phase inverter in DG to operate
in both islanded and grid-tied mode, with no need for switching between two
different control architectures or critical islanding detection. A novel
voltage controller is presented. It is inactivated in grid-tied mode, and the
DG operates as a current source with fast dynamic performance. Upon the utility
outage, the voltage controller can automatically be activated to regulate the
load voltage. Moreover, a novel load current feedforward is proposed, and it can
improve the waveform quality of both the grid current in grid-tied mode and the
load voltage in islanded mode. The proposed unified control strategy is
verified by the simulation and experimental results.
REFERENCES:
[1]
R. C. Dugan and T. E. McDermott, "Distributed generation," IEEE
Ind. Appl. Mag., vol. 8, no. 2, pp. 19-25, Mar./Apr. 2002.
[2]
R. H. Lasseter, "Microgrids and distributed generation," J. Energy
Eng., vol. 133, no. 3, pp. 144-149, Sep. 2007.
[3]
C. Mozina, "Impact of Green Power Distributed Generation," IEEE
Ind. Appl. Mag., vol. 16, no. 4, pp. 55-62, Jul./Aug. 2010.
[4]
IEEE Recommended Practice for Utility Interface of Photovoltaic(PV) Systems,
IEEE Standard 929-2000, 2000.
[5]
IEEE Standard for Interconnecting Distributed Resources with Electric Power
Systems, IEEE Standard 1547-2003, 2003.
